ecological impact of tropical pastures and the potential...

Ecological Impact of Tropical Pastures and

the Potential of Forage Plants for

Sustainable Land Use Systems in the Tropics

An Annotated Bibliography

A. Christinck, K. Probst, R. Schultze-Kraft

Contents

1 Abstract 2

2 Introduction 3

3 Forage plants and pastures within tropical farm ecosystems 4

3.1 Soil properties 43.1.1 Soil chemical properties 43.1.2 Soil physical properties 83.1.3 Soil biological properties 9

3.2 Nutrient cycling 10

3.3 Erosion control 13

3.4 Microclimate 16

3.5 Diseases, pests and weeds 17

4 Tropical pastures within regional and global ecosystems 20

4.1 Hydrology 20

4.2 Regeneration of degraded land 22

4.3 Biodiversity 24

4.4 Atmosphere and global warming 27

5 Conclusions 31

6 References 33

7 List of keywords 144

Chapter 1: Abstract2

1 AbstractThis annotated bibliography lists and summarizes the most relevant references on theecological impact of pastures and forage plants in tropical land use systems. It attempts toprovide knowledge from ecosystem and ecology-relevant disciplines to researchers anddevelopment workers.

The bibliography is structured into different sections, considering on the one hand researchresults at farm-ecosystem level, and on the other hand studies at the regional and global level.Numerous reports are presented on the cultivation of multipurpose herbaceous and woodyforage plants and their effects on soil properties, nutrient cycling, erosion, microclimate, andphytosanitary aspects. On a regional and global level, focus is given to hydrological aspects,the regeneration of degraded land, biodiversity, and climate.

The review indicates that basic data on ecological effects of pasture establishment andlivestock production are still scarce. This is the case in particular for long-term effects at theregional and global levels. Areas of future research are suggested. For a successfuldevelopment of sustainable land use systems interdisciplinary and interinstitutionalcollaboration is indispensable.

Chapter 2: Introduction 3

2 IntroductionIn view of the growing human population and progressive degradation and destruction of thenatural resources, the search for sustainable land use systems is one of the most importantchallenges of our decade. Farming practices and livestock production are generally known tocontribute on a large scale to environmental degradation if they focus on short-termproductivity only.

The aim of this study is to summarize current, tropical-pasture related knowledge fromdifferent ecosystem and ecology-relevant research fields. A second aim is to encourageinterdisciplinary research for developing sustainable farming systems that make use of thepotential that tropical pasture plants are suggested to offer for a wide range of ecological andsocio-economic conditions.

The bibliography is structured into different sections, considering research at farm-ecosystemlevel on the one hand (soil properties; nutrient cycling; erosion control; microclimate;diseases, pests and weeds), and studies at the regional and global ecosystem level on the otherhand (hydrology; regeneration of degraded lands; biodiversity; atmosphere and globalwarming). Each section consists of a summarizing review giving insight into the subject, themain approaches of current research, and the lack of knowledge. References are numbered andare presented in Chapter 6 in numerical order, including keywords and abstracts. The list ofkeywords (Chapter 7) was especially prepared for this bibliography and does not necessarilyrepresent the keywords given in common databases (e.g., CAB-Abstracts, TROPAG,Agricola). If a reference lacked an abstract or summary, an own abstract was added and isidentified as such („Abstract by bibliography authors“).

The study is based on an effort to gather relevant literature that was readily accessible in 1995but by no means do the authors claim the bibliography to be complete. The intention is ratherto provide a starting point for subsequent, exhaustive literature searches within the nineindividual research areas that are outlined in this study.

Chapter 3: Forage plants and pastures within tropical farm ecosystems4

3 Forage plants and pastures within tropical farm ecosystems

3.1 Soil propertiesAlthough a wide range of soil types are found in tropical regions, highly weathered and low-activity clay soils (Ultisols, Oxisols and Alfisols) in tropical forest and savanna regions are themost important groups used for farming, generally because of the favorable topographic andclimatic conditions in the respective regions {1, 2}. Ultisols and Oxisols are strongly acid andleached soils with low cation exchange capacity (CEC), very low inherent fertility, multiplenutrient (N, P, K, Ca, Mg, Zn) deficiencies and nutrient imbalances (e.g., toxic levels of Al orMn). Alfisols which are less acid and have high base saturation, are characterized byinherently low nutrient (N, P, K, S and Zn) status and low structural stability {1, 3}.

Maintaining soil fertility and productivity are the major management problems when thesesoils are used for crop and pasture production {1}. In traditional cropping systems, based onshifting cultivation or bush fallow rotation, soil fertility was regenerated during fallow periodsthrough the activity of trees and other natural vegetation {4, 5, 6, 7, 8}. With the rapidlyraising human population and increasing pressure on cropping land, fallow periods arebecoming shorter so that fertility regeneration is less effective and productivity declines {1, 4,5, 7, 8, 9, 10}.

In recent years, the cultivation of multipurpose herbaceous and woody forage plants becamemore and more relevant to maintain soil productivity in low-input productions systems undershortening fallows {1, 4, 5, 7, 8, 10, 11, 12, 13, 14, 15, 16, 17, 18}. Numerous studies havebeen conducted to assess changes in soil chemical, physical and biological propertiesassociated with the growth of pasture plants in different integrated farming systems.

3.1.1 Soil chemical properties

Nitrogen deficiency is a major cause of declining soil fertility {13, 19, 20, 21}. As N is a veryexpensive nutrient to manufacture necessitating high energy inputs {13, 22} (section 4.4), theuse of leguminous plants as a source of N is particularly interesting in low-input farmingsystems of the tropics {14, 23, 24, 25, 26}.

Leguminous plants used as mulches, green manures, cover crops, or as components ofpastures or fallow vegetation, are generally known to improve soil organic matter (OM) andenhance total-N through symbiotic nitrogen fixation {4, 5, 6, 10, 11, 12, 13, 14, 16, 17, 21, 22,24, 25, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43}. On soils with low Ncontents, the amount of N2 fixed depends largely on the dry-matter production of the plant,which in turn depends on the legume genotype and environmental conditions during growth

Soil properties 5

{1, 13}. Annual N yields of tropical forage legumes with average growth range from 30-400kg/ha (1, 22, 33, 34).

However, when using legumes to improve soil total nitrogen content, it should be rememberedthat:

• Not all legumes can associate with rhizobia {7};

• legumes fix N2 in inverse relation to the amount of nitrogen available in the soil. In soilswith moderate to high levels of available N, soil improving legumes are of little value{24};

• the growth of legumes depends on the presence of a suitable rhizobium strain; inoculationmay be necessary {7};

• growth and also N2 fixation can be hindered by an unfavorable pH {32, 44} and/or lack ofother nutrients (particularly P, Ca, Mo, Zn) or by Mn toxicity {7, 34};

• environmental conditions such as irradiation have to be favorable to ensure adequateproduction of carbohydrates in the plant's leaves and their downward translocation to thenodules {13}.

If N2 fixation and nodulation of legumes was significantly reduced, a greater demand on soilN was frequently observed, possibly leading to competition for N between legumes andassociated crops {13, 45}. Another source of N is N2 fixation through associative symbiosisbetween grasses and bacteria (e.g., Azotobacter paspali, Azospirillum brasiliense, Beijerinckiaindica, Enterobacter cloaceae). There are indications that the amounts of N2 fixation achievedunder grass can be as high as 45-100 kg/ha {9, 35, 46}.

A proportion of the plant litter N becomes 'stable' and might not be available for re-uptake byplants for several years as it accumulates in soil OM and in living remains {35}: Nitrogen inmaterial with less than 1.0-1.5 % N is largely immobilized in tissues of the decomposingmicrofauna and becomes available to plants only slowly, whereas in material with higher Nconcentrations a proportion of N is in excess of requirements for microbial growth and isreleased to the soil ammonium pool {47}.

Decomposition pattern and mineralization of organic matter are essentially determined by theC/N ratio and the content of secondary compounds: N mineralization from C4 grasses isrelatively slow because of their high C/N ratio {31, 46}. A high lignin/N ratio promotes theincorporation of N into stable humic complexes {20}. Polyphenolics which can be common inlegumes growing on poor soils {48}, are highly reactive compounds and can form stablepolymers with many forms of N {23, 48}. Thus legumes and grasses with slow decompositionrates may not provide enough N for plant growth in the short term, but they contribute to thebuild-up of soil organic N and therefore can provide a low but continuous supply of N in the


long run. On the other hand, legumes with low polyphenolic content release N rapidly,providing sufficient N for plant growth, but nitrogen may be lost by leaching of nitrate ( NO3

− ){23, 31, 46}.

Drying and wetting generally leads to accelerated release of N, too. This may be ofsignificance in areas with a pronounced dry season or when supplementary irrigation is given{46}.

Besides N, forage legumes and grasses in alley cropping, mulching systems {1, 4, 14, 15, 28,39, 49, 50}, in ley farming {9, 46, 51, 52,} and cultivated fallows {5, 7, 12, 36} also mobilizelarge quantities of other nutrients. In the long run, soil fertility is built up through enhancednutrient uptake from subsoil resources (e.g., Mg, Ca, K, P) and accumulation of OM. OMprovides most of the CEC in highly weathered soils and, besides supplying N, it is animportant slow-release source of sulphur and phosphorus {33, 46}. In tropical soils,phosphorus is a rather immobile element as it is absorbed by Fe and Al oxids on the surfacesof clays and precipitated by Fe and Al cations to form insoluble Fe or Al phosphates {53}.Vesicular-arbuscular mycorrhizae (VAM), which form symbiotic associations with roots ofmany forage plants, help to increase P uptake from soils poor in phosphorus {2}. Thus,phosphorus may be concentrated in plant biomass and will become more available afterdecomposition {2, 46}. The order of nutrient release from leguminous litter seems to followthe general trend potassium > phosphorus, nitrogen, magnesium > calcium. The initialimmobilization of calcium is generally attributed to accumulation of calcium oxalate in thefungi that colonize decomposing leaf tissue {48}.

Under temperate-climate conditions, accelerated soil acidification has been observed whereimproved pastures of annual grasses in mixture with legumes (e.g., Trifolium subterraneum)have been grown continuously for 25 to 50 years {27, 54}. During acidification the basesaturation (Ca++, Mg++, K+, Na+) is decreased and the proportion of CEC occupied by H3O+

and various forms of Al is increased {27}. Particularly in south-eastern Australia and someareas of New Zealand, the gradual decline in soil pH under leguminous pastures has causedconsiderable concern as manganese and aluminum have increased to phytotoxic levels.Applications of lime to neutralize acidity have become an important part of pasturemanagement in these regions {27, 54, 55, 56, 57, 58, 59, 60}. Much of the accelerated soilacidification in pasture soils has been caused by increasing nitrogen inputs through N2 fixationand fertilizer use {19}.

Major processes leading to acidification during N cycling (see section 3.2) in soils are {27, 54,59, 56}:

- The excess uptake of nutrient cations over anions by N2 fixing legumes with a consequentnet efflux of protons (H+) into the rhizosphere;

Soil properties 7

- the net nitrification of N derived from fixation (NH 2O NO H O 2H );4 2 3 2+ − ++ → + +

- loss of N through leaching of nitrate;

- removal of plant and animal products.

Apart from climatic conditions and the buffering capacity of the soil, the degree to whichacidity develops will depend upon the growth rate of the legume, the extent of N2 fixation, therelative cation requirements as well as the form and amount of amino acids and organic acidssynthesized within the plant {27, 54}.

There are indications that tropical legumes may have a lesser acidifying effect than temperatespecies: Part of the reason is that their NH3 assimilation products appear to be ureides(allantoin, allantoic acid) which are unlikely to dissociate within the plant and to donateprotons, whereas in most temperate legumes NH3 is assimilated into the easily dissociatingcarboxylic acids, aspartate and glutamate. The H+ ions produced by dissociation of organicacids within temperate legumes have to be exported into the rhizosphere in order to maintainthe plant's internal pH balance {54}. Moreover, many tropical legumes have evolved in acidicsoil environments and therefore have generally lower cation levels (Ca++ and K+) in theirtissues {27}. Thus, the excess of cations absorbed seems to be less for tropical than fortemperate legumes, so that the former species do not apparently acidify their rhizosphere asmuch as do temperate species when actively fixing N2.

In contrast to temperate leguminous plants, the growth of grasses absorbing nitrate (byexchange of OH- or HCO3

− generally tends to raise soil pH {9, 27, 46, 61}. In addition, theleaching loss of nitrate ( NO3

− ), which is another major process with a net acidifying effect onthe soil {27, 54}, can be reduced by growing perennial grass species with a continuouslyactive, dense root system {27, 58, 59}. The leaching of NO3

− in temperate leguminouspastures is often in the order of 8 to 10-fold greater than under pure grass pastures. In thecourse of this process exchangeable cations may be moved downwards as counterions withNO3

− resulting in a decrease of base saturation {27}. Hence, the effect of a grass-legumepasture on soil acidity and fertility will depend to a large extent upon the ratio of grasses tolegumes present {27}.

Most of the studies concerning legume-induced soil acidification have been conducted intemperate regions. However, recent work indicated that degradation of soil throughacidification might also be a problem in tropical agriculture {56, 62}. Thus, further researchwill be necessary to clarify the long-term effects of legumes and grasses on pH of poorlybuffered tropical soils.


3.1.2 Soil physical properties

The maintenance and improvement of the soil structure are important for sustainableagriculture. In addition to pedogenetic and climatic factors, farming practices such as tillage,crop rotation, grazing and manure application influence both the form and stability of soilstructure {63}: As cultivation and tillage operations are usually accompanied by a decline inOM and by subsequent mineralization {9, 46}, arable cropping tends to destroy soil structure,to decrease total porosity and to increase soil bulk density. This may in turn cause a decline inrainfall infiltration rate {9}, thereby increasing the rate of soil erosion. Also trampling bygrazing cattle can contribute significantly to soil compaction (see section 3.3).

Apart from applying repeatedly high doses of organic manures and mulching material {64}, arest period under grasses or/and leguminous cover crops is the best means of increasingorganic matter and improving physical conditions of arable top-soils {46, 65}. By addingorganic matter, providing a good canopy cover and by loosening the soil surface throughvigorous rooting, pasture plants and woody perennials help to improve soil structure (increaseof aggregate size and stability, porosity, permeability; decrease of soil bulk density) and soilmicroclimatic parameters (increase of water holding capacity and soil aeration, decrease ofsoil temperature) (section 3.4) {9, 10, 28, 31, 33, 36, 46, 51, 63, 64, 65, 66, 67, 68}.

Some studies indicate that grasses appear to be more effective than legumes in improving thesoil structure and in restoring the OM level, as the N-rich leguminous plant material oftendecomposes more rapidly {31, 46, 65}. Soil under grasses contains some of the highestconcentrations of roots of any agricultural system: Natural grassland soil may contain over12 t of roots/ha, compared with only 2-5 t/ha of above-ground material {46}. The roots ofBuffel, Rhodes, Kikuyu grass and Themeda can grow as deep as 6 m. When these roots aredecomposed, they produce channels through which water can move into deeper soil layers{46}.

In addition, grass roots can be particularly strong stabilizers of soil aggregates for reasons thathave not been fully explored. Probably fungal hyphae and gum-producing bacteria in therhizosphere of some grasses are involved in holding soil crumbs around grass roots {46}.Further research is needed to reconsider if grasses generally have higher potential for soilstructure formation than legumes, and which parameters are decisive in this regard (e.g.,rooting pattern, C/N ratio, lignin content, polyphenolics, microorganisms etc.).

Improvements of soil structure increase the amount of water available for crops. Theyimprove aeration and drainage and encourage root growth {46}. These benefits may have onlysmall short-term effects on yield, but they provide ecologically more sound conditions forcrop growth and help to reduce erosion {46, 64}.

Nutrient cycling 9

However, the soil physical improvements achieved by mulching or during a rest period undergrass and legumes are rapidly lost during subsequent arable cultivations. In order to plansustainable crop rotations the rate of deterioration of soil structure during the arable period isas important as its rate of restoration; it requires further critical examination {46, 65}.

3.1.3 Soil biological properties

As plant residues provide the main food for many soil organisms {46}, pasture plants arelikely to have a significant effect on soil biological activities. An increased primaryproductivity of improved pastures and a higher nutritional value of the sown plants {69} mayenhance the activity and number of both soil micro- and macroorganisms.

Decomposers, feeding on dead organic matter, comprise the greatest bulk of grassland soilfauna. The predominance of this trophic group reflects the high rate of return of dead organicmatter to the soil in most grasslands {70}. Microbial activity of agriculturally importantorganisms such as N2 fixing bacteria and VAM is generally greatest in the plant rhizosphereand seems to be stimulated by the abundance of organic substances supplied as root exudatesand decomposing roots {46}.

Among the macrofauna, earthworms are often the most abundant as well as the most obviouszoological component of soils and therefore have been the subject of a considerable amount ofresearch, especially in the palearctic region {71}. Several physical and chemicalenvironmental factors have been suggested as determinants of the distribution and abundanceof this group of animals. These include available moisture, temperature, soil texture, soildepth, quantity and persistence of organic matter, secondary compounds, C/N ratio, calciumcontent and pH {67, 70, 72, }. As discussed above (see sections 3.1.1 and 3.1.2), most of theseparameters are substantially influenced by vegetation. A number of studies confirm that thegrowth of leguminous cover crops and grasses {1, 28, 33, 67} as well as the use of dung {71,73} increase earthworm activity.

However, little research has been done to investigate the interactions and relationshipsbetween particular pasture species and the soil fauna. The greater number of publications hasbeen concerned rather with the role of soil organisms in soil improvement and nutrientcycling, which in turn improve plant growth and crop yield (see section 3.2). Though there isno doubt that soil biological processes are of utmost importance to soil fertility andsustainable plant production, the complex interactions between plants, soil fauna andenvironmental parameters (including management practices) are still rather unexplored andhence deserve more attention in future research.


3.2 Nutrient cyclingIn low-fertility soils, nutrient cycling is an important basis for sustainability {2, 23, 74}. It isthe main reason why acid, infertile Oxisols and Ultisols are able to support exuberant tropicalrainforest vegetation in udic environments {2, 53}. The majority of the nutrients in theseecosystems is stored in the living biomass and detritus (fallen leaves, residues from forest andanimals), whereas nutrient amounts in the soil deposit are rather low {3, 53, 75, 76}.

The conversion of such a natural ecosystem, which is in equilibrium with regard to nutrients,into an agro-ecosystem with a totally new set of inputs and outputs, will inevitably lead to achange in nutrient fluxes {62}. When forests on poor soils are cleared and burned, nutrientcycling mechanisms are destroyed or interrupted and the non-volatile elements in vegetationare released to the soil {53, 75}. As a result the soil undergoes dramatic increases in K, Ca,Mg, NO3

− {77}, available P, and pH, as well as a reduction in Al saturation {3, 38, 74, 76}.This high initial fertility after burning decreases rapidly because of nutrient losses throughleaching and erosion if the forest is replaced by highly extractive systems and if the soilsurface has only a sparse or temporary cover as in the case of arable cropping {53, 78}.

However, the replacement of forests by agroforestry systems or well-managed pastures with adense and constant soil coverage may provide a recycling process similar to that of nativevegetation {53, 74) although the amount of nutrients recycled in pasture ecosystems isconsiderably less than in an intact forest {74}. Like a forest, pasture systems store nutrients inboth the living and dead biomass, and in the soil. Rain carries atmospheric dust and N, andpromotes the incorporation of nutrients into the soil {53, 74}. Pastures containing legumesbenefit from fixation of atmospheric N, and it seems that legume contents of 20-45 % ofherbage dry matter could provide enough nitrogen to maintain a productive and sustainablepasture {35}.

In a pasture, nutrients are taken up by plants from litter and soil, and are subsequentlytransferred to grazing animals. Man removes part of the nutrients in the form of animalproducts, and the rest should return to the soil in the form of faeces and urine {53, 74}. Cattledetritus as a nutrient cycling pathway differs from litterfall in that (i) nutrients are morechemically mobile and (ii) patchily distributed. Dung and urine produced by cattle makenutrients readily available for plants enhancing productivity {46, 76, 79}, but excretion mightalso be associated with greater losses {35}. Thus, compared to an ungrazed ecosystem, grazedgrasslands have a more rapid turnover of vegetation and nutrients {76, 80}.

Plant and animal remains decompose and are incorporated as organic material into the soil,thereby enhancing the quantity of nutrients available {74}. To study the fate of N in plantresidues during their decomposition, 15N-labelled plant material is used {47}.

Nutrient cycling 11

Among the animal remains, the value of invertebrate residues (corpses and excreta) which areavailable for decomposition and mineralization should not be underestimated concerning theircontribution to the soil nutrient status, especially to the phosphorus economy in pastures {81}.Apart from the formation of nutrient rich residues, the net functional contribution ofinvertebrates to nutrient cycling depends largely on their ability to stimulate microbial activity.Several studies of invertebrates and their interactions with microorganisms demonstrate theregulatory roles of invertebrates in nutrient cycling:

Earthworms, which in humid tropical grasslands can reach population densities of severalhundred individuals/m2 with a biomass up to 60 g/m2, play a major role in creating andmaintaining soil fertility through litter ingestion, burrowing and soil mixing {70, 71, 81, 82}.By their burrowing activities earthworms incorporate plant remains from the litter into thesoil. They increase the total pore space as well as the proportion of larger pores within the soiland thereby influence its drainage, aeration and infiltration characteristics {71, 81, 82}. Boththe burrowing and feeding activities of these animals produce large amounts of faecalmaterial. Earthworm casts are the solid remains resulting from these activities that aredeposited at the soil surface. These casts have been shown to contain more water-stableaggregates and to be microbially more active than the surrounding soil. Due to this enhancedmicrobial activity within the cast material, earthworms help to increase the availability ofnutrients {71, 81}.

Where worms are not present in pastures, dense mats of dead and decaying root material mayaccumulate at the soil surface, 'locking up' large quantities of valuable nutrients {71}. Theintroduction of earthworms to such unpopulated soils, for example in New Zealand, or intopolder grassland in the Netherlands, has led to significantly higher grass production withinitial yield increases of greater than 70 per cent {20, 71, 72}.

In drier tropical soils, termites usually are the dominant macroinvertebrates. Termites andother arthropods, notably ants, mites, centipedes, isopods and collembola, help to fragmentplant residues and hence increase the surface area available for microbial colonization andmineralization {70, 81}. If food is scarce, there can be a competition betweenmacroinvertebrates and soil microorganisms for the exploitation of the more easily digestibleand energy rich substrates. On the other hand, the macrofauna can also benefit from microbeswhen they feed on degradation products such as cellulose or hemicellulose which the formercannot digest themselves {82}.

The consumption of microbes has an important role in nutrient cycling through lysis of theingested organisms and excretion of formerly immobilized nutrients {70, 81}. Microbivory,however, can also have negative effects on the nutrient balance. For example, it has beenfound that some collembola reduced the phosphorus uptake and growth of plants by feedingon the external hyphae of a mycorrhiza endophyte {81}.


The soil nutrient status will decline if the outputs in plant and animal products {83} and thelosses in erosion, runoff, leaching and atmospheric gasses exceed the inputs to the soil in theform of fertilizer, weathering of rock, atmospheric accession and fixation {62}. The majorityof studies that have been conducted to investigate and to quantify nutrient fluxes in agro-ecosystems, focus on processes within the carbon cycle and particularly the nitrogen cycle. Inaddition to the agronomic importance of these cycles there are also environmentalimplications, which explain the great interest in this area, such as nitrate leaching {27, 62},N2O production during denitrification under oxygen-limited conditions {73, 84, 85}, and acidproduction through incomplete nutrient cycling {54, 59, 62}.

Acids are produced in many of the nutrient cycles, but the main acid production in pastureecosystems occurs in the carbon and nitrogen cycles {60}. In the carbon cycle, acids areproduced in association with increases of OM, with the removal of plant material and animalproducts, and with transfer of dung and urine to stock camp areas of paddocks. Pastureimprovement through fertilizer applications or introduction of legumes may contribute toincreased OM accumulation and higher animal production associated with increased stockingrates and consequent higher product removal {59}. In the nitrogen cycle, inputs ofsymbiotically fixed N, ammonium fertilizers and losses of nitrate by leaching are involved inaccelerated acidification of agricultural soils {54, 59}. In north-eastern Victoria (Australia),carbon and nitrogen cycle acidification accounted for 65 and 35 %, respectively, of the netacid addition on a fertilized pasture {59}.

The production of gaseous N compounds is potentially one of the most important routes of Nlosses from pastures {85} as well as from tropical forest soils, where measured fluxes of N2Ohave been substantially greater than from temperate or boreal forests {84}. In well-drainingsoils, denitrification generally occurs under anaerobic conditions in microsites of highcontents of labile C and mineral N. Research conducted under temperate climatic conditionsrevealed that earthworm casts and burrow walls which generally have higher ammoniumconcentrations, labile C, and water holding capacity than bulk soil samples, constitute sites ofhigh denitrification potential and also influence nitrate leaching patterns {73, 85}.

Soil management practices in low-fertility soils should encourage nutrient cycling as much aspossible {2, 53}. Effective soil fertility conservation may require that cycling components andmechanisms are introduced into agricultural systems {75}. Management options exist toimprove nutrient cycling and the productive stability of agro-ecosystems, for instance:

• Nutrients should be returned to the production cycle by minimizing dung transfer, reducinghay cutting, leaving harvest residues in the field, using different forms of fallow etc. {7,59};

• the inclusion of trees and shrubs acting as nutrient pumps helps to transfer (via fallingleaves) nutrients to the soil surface that had percolated to the subsoil or that were released

Erosion control 13

in the rock weathering zone {2, 7, 49}. Secondary species may cycle nutrients at higherrates than climax species {75};

• biological N fixation by symbiotic or non-symbiotic microorganisms should be promoted(e.g., by mixed cropping, inoculation, adding micronutrients etc.). The use of VAM couldresult in higher yields on P-fixing soils {7, 74}.

In spite of optimum management practices, it is often necessary to replace nutrient lossesthrough periodic fertilizer applications {7, 62, 74}. Additional data are required on the spatialand temporal variation in recycling processes in order to develop management strategieswhich allow a better synchronization between the supply of nutrients from all sources, andplant requirements {35}. To fully appreciate the extent of degradation of soil fertility undercurrent farming practices and the potential role of pastures, we need better nutrient balancestudies considering the different environments and climatic conditions. There is an urgentneed to quantify nutrient fluxes, including annual emissions of gaseous compounds, nutrientinflux through deposition of atmospheric dust, rates of organic matter decomposition etc.

3.3 Erosion controlLosses of topsoil through erosion depend mainly on soil properties, topography, climate andland use {86, 87, 88}. In dry areas, wind is a major cause of erosion {89, 90}, whereas inhumid tropical and monsoonal regions intense rainstorms are leading to severe erosionproblems {32, 46, 86, 91}. Water runs off the surface when the rate of rainfall exceeds the rateof infiltration. This may imply loss of much-needed water and of valuable topsoil threateningthe long-term productivity of arable land {46, 92, 93}.

Deforestation, shifting cultivation, the use of steep slopes for cropping, reduced fallowperiods, cutting of woody perennials to obtain fuelwood and forage, as well as overgrazinghave resulted in increased erosion problems throughout the tropics {15, 87, 88, 89, 94, 95, 96,97}. Undoubtedly, pastoral activities have contributed on a large scale to degradation of thesoil resource. Severe changes in composition of plant communities may occur under heavygrazing {87, 98}. With increasing grazing intensity, a shift from shrubs and perennial grassesto annual grasses and forbs is frequently observed, and removal of perennial plants is usuallyassociated with increased erosion {87, 97}.

Moreover, trampling by stock has been shown to reduce infiltration rates by promoting soilcompaction and surface sealing {56, 78, 87, 99, 100, 101, 102, 103}. Seed removal duringrunoff, high temperatures, low water content in the sealing surface, and mechanical impedancesubsequently prevent seedling emergence, thereby increasing erosion and desertification {56,87, 96}. The sparse vegetative cover left by livestock finally might be removed by termites,


microorganisms and rapid phytomass decomposition due to high temperatures, creating anenvironment highly susceptible to erosion {33, 87}.

Cropped hillsides with slopes between 18-50 % are generally most severely eroded {15}. Astudy conducted in a mountainous area of Peru revealed that after changing land use fromforest to crops or pasture, the suspended-sediment concentrations in the streams of therespective watershed increased significantly. This study confirmed the importance ofmaintaining a forest cover for soil protection on slopes steeper than 40 % {86}.

In this context, tree crops are generally suggested to be ecologically suited to the tropicalenvironment causing little or no damage to soil {1}. However, the erosive energy of rain mayincrease under a high tree canopy through coalescence of raindrops into larger drops to such adegree that high erosivities have also been recorded under forest plantations {90}.

All soil conservation practices in tropical agriculture emphasize the need for good groundcover and the addition of OM which is known to have a favorable effect on soil physicalproperties (section 3.1.2) {15, 33, 46, 88, 104, 105, 106} as well as soil biological activities,e.g., the presence of earthworms (section 3.1.3) {33, 90, 104, 105}. Improvements of the soilstructure will permit more water to penetrate and will store or drain any excess {46}. Thus, bydecreasing the amount of run-off water, the transport of fine particles and the loss of nutrientswill also be reduced {15, 46, 86}.

During recent years there has been an increasing interest in the introduction of herbaceous andwoody forage plants in crop production systems as sources of mulch, green manure, groundcover, supplementary browse, contour hedges and windbreaks in order to control erosion {1,9, 15, 32, 33, 37, 90, 95, 96, 104, 105, 236}.

The use of shade-tolerant, creeping leguminous covers (e.g., Pueraria phaseoloides,Desmodium ovalifolium, Centrosema pubescens, Calopogonium mucunoides) has become astandard practice in several plantation crops such as rubber, coconut and oil palm {33, 46,237}. The legumes are expected to quickly provide a dense vegetative cover of the soil andthus to decrease the erosive energy of raindrops. By shading the soil they reduce soiltemperature and the decomposition rate of organic matter, which helps to improve soil texture,water infiltration and water holding capacity {33}. Weeding activities, through which soilsurface is disturbed and exposed to erosion, are not necessary if a cover crop smothers weedssuccessfully {1, 33, 104}.

The concept of leguminous ground cover in tree plantations led to the idea of "living mulches"(intercropping) in food crop production {1, 32, 37, 51, 92, 104}: The "live-mulch system" is acrop production technique in which food crops are planted directly in a low-growing covercrop (Centrosema pubescens, Psophocarpus palustris, Vigna trilobata etc.) with minimumsoil disturbance {1}.

Diseases, pests and weeds 15

Short-term fallows with pasture plants and subsequent (chemical) killing of the vegetativecover provide another method to grow arable crops, possibly with no-tillage cultivation. Thekilled sod mulch has proved to be effective in controlling soil erosion {1, 67}.

Not only herbaceous, but also woody forage species can be instrumental in erosion controlwithin (integrated) farming systems: On rangeland, microsite soil enrichment through litteraccumulation in the immediate environment of woody species {66, 90, 105} may beimportant, as biomass in the shrub understorey aids infiltration and decreases run-off,especially beneath thorny shrubs where livestock grazing is restricted {87}.

A large amount of studies have been carried out on alley cropping, an agroforestry system inwhich arable crops are grown between hedgerows of woody shrub or tree fallow (e.g.,Leucaena leucocephala, Gliricidia sepium, Flemingia macrophylla (syn. F. congesta),Sesbania spp., Albizia spp., Calliandra spp., and Populus spp. and Salix spp. in highlandregions). The hedgerows are pruned periodically during the cropping season to provide greenmanure for the companion food crop {1, 15, 96, 105}. In situations where soil conservation(erosion) is considered a major issue, high foliage productivity coupled with a slowdecomposition rate of foliage are advantageous characteristics of hedgerow species {105},due to great effects in reducing erosion by maintaining a ground surface cover of litter andmulch {90}.

In addition to maintaining soil cover and improving soil physical structure, the formation ofdense vegetation barriers is a desirable option in soil and water conservation: In alley croppingsystems on steep slopes, hedgerows planted along the contours provide a biophysicalinfrastructure within which cropping can be carried out without danger of massive soil erosion{15, 90, 96, 105}. The distance between hedgerows should be adjusted to the slope degree:the steeper the slope, the narrower the interspaces with arable crops {15}. It is generallyobserved that in about three years of continuous cultivation the strips between hedgerowslevel off, becoming a series of natural terraces {15, 95}. Such terraces can be stabilized byrocks and stones at the base of the hedgerow, or by planting additional grass strips {15}.

Where wind is a major cause of soil erosion, windbreaks can make sustainable productionpossible. Windbreaks (shelterbelts) usually consist of (several) multistorey strips of trees,shrubs and/or grasses planted perpendicular to the prevailing wind. They can reduce thevelocity of wind and thus its ability to carry or deposit soil and sand, which might lead tosandblasting or burying of crops {89, 90, 107}. Windbreaks have to be designed andmaintained semi-permeable for good function. Otherwise (very dense structure or gaps), theymight promote erosion by creating strong turbulences or channeling the wind, actuallyincreasing its velocity. A properly designed windbreak can protect a field at least 10 times aslong as the height of the tallest trees {90}. Even windbreaks with predominantly low growingherbaceous vegetation (Cenchrus biflorus, Cassia mimosoides, Stylosanthes spp., Andropogon


gayanus) can create a rather homogenous obstacle and effectively reduce wind speed and theamount of air-carried soil particles {89, 108}.

3.4 MicroclimatePlant communities have a substantial influence on climatic conditions close to the soil surface{109}. In the tropics, reduced temperature and increased moisture availability in the upper soilstrata are particularly important in relation to early plant development (germinating seeds,sprouting in vegetative propagation), growth of superficially rooting species and nitrogenfixation in root nodules {64}.

Microclimatic conditions are to a considerable extent related to the transmission of solarradiation by the plant canopy. The different illumination of soil by solar rays under vegetationcauses differences in temperature and humidity of the air and soil, depending on canopystructure and density {109}. Cover crops shade the soil from direct sunlight and thereby aid toreduce soil evaporation, to lower soil temperature and to keep down the rate of decompositionof organic matter {33, 110}. Topsoil temperatures (2.5 cm depth) dropped, for instance, from42°C in bare soil to 25°C under a grass cover of 25 cm height {46}. Also the daily range oftemperature variation under plants is generally lower than in open areas {109}.

Conversely, herbage removal, e.g., through grazing, may encourage evaporational loss andcreate a lighter, warmer and drier microenvironment. This is probably one reason why effectsof drought and overgrazing tend to be confounded {98}. Fast-growing and deep-rootinggrasses and cover crops with high rates of transpiration may cause a strong demand on soilwater and can dry out the soil to a considerable extent. This can lead to adverse effects,especially in arid environments {46, 90}. Thus, establishing plants for improvement ofmicroclimatic conditions in particularly difficult, arid environments requires careful selectionof suitable species.

The accumulation of organic matter contributes greatly to soil moisture conservation.However, mulch materials have different capacities in terms of soil temperature reduction,moisture conservation and duration of these beneficial effects {50, 64}:

• Voluminous layers (e.g., mulch of Flemingia macrophylla) trap considerable quantities ofair which form a barrier to heat transport and evaporation of soil moisture;

• dark-colored surfaces (such as Leucaena leucocephala mulch) absorb more radiationcompared to lighter-colored surfaces. As a consequence, temperatures under dark mulchlayers are relatively higher;

• the chemical composition (C/N ratio, lignin, polyphenolics) is an important factor thatdetermines the effective life-time of a mulch material and hence the longevity ofmicroclimatic improvement {64}.

Microclimate 17

Further research is needed to determine and to quantify the effect of pasture plants andmulches on microclimatic parameters and to assess the importance of these parametersregarding plant growth, soil biological activities, and incidence of pests and diseases.

Shading by trees and shrubs is not only for the benefit of cattle, but may also stimulate pastureproductivity {20, 109, 111, 112}. For example, Paspalum notatum under Eucalyptus grandistrees has been shown to be more productive than grass without shade, and Panicum maximumyielded more under a canopy of Albizia lebbeck than it did in the open {20}. The mechanismsfor this response are not yet clear, although there are suggestions that water availability maybe an important factor {20}.

Tree and shrub plantings have a noticeable effect on the redistribution of precipitation andthereby influence the distribution of moisture within the soil profile: Generally, the windwardside of soil under trees is more heavily moistured than that of the leeward side, and the depthof wettening the soil is particularly high under the trunk due to runoff {109}. Furthermore,multistorey strips of trees and shrubs as well as herbaceous vegetation, provide effectivewindbreaks. By lowering the wind speed, evapotranspiration is reduced in the protected area.However, despite reduced potential evaporation, subsoil water reserves may decline if thewindbreaks are narrow-spaced and vegetation consumes large quantities of water {89, 90}.

For successful exploitation of potential microclimatic improvements through trees, shrubs andpastures, further information is required on the physiology, water economy and canopystructure of eligible species as well as on suitable planting patterns to minimize competitionfor water, nutrients and light.

3.5 Diseases, pests and weedsDiseases, pests and weeds can be controlled chemically, biologically, culturally andgenetically {113}. Because of the potential adverse impact of pesticides on fragile ecosystems,integrated control strategies based on agronomic management, host plant resistance andbiological control agents should be given preference {114}. The use of pasture plants inintegrated farming systems offers a range of possibilities to control phytosanitary problems bycultural and biological means:

Several studies indicated that certain leguminous cover crops and grasses (e.g., Cynodon spp.)have potential for management of nematode populations in susceptible crops {9, 115, 116,117, 118, 119}. When Pueraria phaseoloides, Arachis pintoi, and Centrosema pubescenswere co-cultivated with tomato in greenhouse pot tests, a significant reduction in gallingcaused by Meloidogyne arabicida was observed in tomato {117}. Planting Aeschynomeneamericana and Indigofera hirsuta in rotation with soybean reduced juvenile populations ofMeloidogyne arenaria and Heterodera glycines at the end of the season; however, this


suppressive effect was short-lived {116, 118}. Also green-manuring with some cultivars ofCajanus cajan and Crotalaria spectabilis seems to be a suitable way to reduce populations ofthe root-knot nematode Meloidogyne incognita {119}.

As in the case of nematodes, the severity of soil-borne fungal diseases often depends oncropping history. Ley pastures may help to break disease cycles {43}. Experiments conductedin Queensland (Australia) revealed that common root rot in wheat, caused by Bipolarissorokiniana (= Cochliobolus sativus), was less severe when wheat was planted after Medicagosativa, M. scutellata and Cenchrus ciliaris, than when it was grown continuously {120}.

Some tropical legumes even may serve for control of insect pests: Freshly cut leaves ofjackbean (Canavalia ensiformis) can be used as a biological control agent for leaf-cutting ants(Atta sp.) as they contain the fungicide demethylhomopterocarpin affecting the ants' fungusgardens {121}. Another strategy to reduce pest populations in certain crops is the use of trapplants. Indigofera spp. might be suitable trap plants for Piezodorus guildinii (Heteroptera:Pentatomidae), a neotropical stink bug, thereby reducing the impact of this pest on soybeancrops {122}. Some cultivars of the commercially important genus Stylosanthes have beenshown to trap host-seeking larvae of the cattle tick Boophilus microplus and could provide ameans of controlling cattle ticks in improved pastures {123}.

Creeping leguminous cover crops which grow rapidly and vigorously (Centrosema pubescens,Pueraria phaseoloides, Mucuna pruriens and Desmodium ovalifolium) help to eliminateweeds and to reduce weed seed banks {1, 18, 124}. Today, such cover plants are widely usedfor weed suppression in tree plantations {33, 46}. Even very aggressive weeds such asImperata cylindrica may be controlled by using Pueraria phaseoloides, Stylosanthesguianensis and Calopogonium mucunoides {1}.

Mulching showed promising results in retarding weed development, too. However, the valueof mulching seems to be limited to the control of weed species that were multiplied by seed,whereas regrowth from roots or stumps from former vegetation is unlikely to be suppressed bya mulch layer {125}. Biochemical interactions such as allelopathy seem to be involved in theability of pasture plants to suppress weed growth {126}.

The use of pasture plants seems to be very promising for management of phytosanitaryproblems in integrated farming systems and therefore deserves more attention in futureresearch. On the other hand it cannot be ignored that in recent years an increasing number ofpathogens and pests has been identified on tropical forage plants {113, 127}. If such parasitespossess a wide host range, they might affect associated crops {128}.

Phytosanitary problems are more common in agroecosystems than in natural, diverseecosystems. Therefore pasture improvement and cultivation of large areas with geneticallysimilar forage plants have increased the potential for losses to pests and diseases {113, 114,

Diseases, pests and weeds 19

129}. There are several publications describing the most commonly found nematodes {130},insect pests {113, 131, 132, 133, 134, 135, 136, 137, 138} and diseases {75, 113, 128, 129,139, 140} associated with tropical pastures. Awareness of the range and distribution ofparasites recorded on pasture plants as well as of potential seed-borne diseases is regarded asessential for preventing global transmission of these organisms {141}. Unfortunately,introduction of contaminated seed is yet rather common {128}. Bacteria and potyvirusesconstitute a particular danger due to the difficulties of eliminating them from seed {129}.

Pests and diseases of pastures can reduce forage quantity and quality. They can even causeundesirable changes in plant persistence and botanical composition of grazing land with long-term effects on productivity {74, 142, 143}. However, caution should be taken in estimatingyield loss and disease severity: For example, herbivorous insects are not generally deleteriousto grassland production. Studies revealed that some chewing and sucking insects, such ashemipterous insects {144} or grasshoppers {145}, may inject growth-promoting substancesinto the plants during feeding, thus stimulating regrowth potential and seed production.

Often, pasture disease evaluation is done in small monoculture plots neglecting that grazingand competition between associated plant species can influence disease development.Heterogeneous perennial pastures grazed by cattle would be a more realistic place for thiskind of evaluation {127, 142}. More information is required concerning ecology and hostplant range of pasture pests and diseases and their practical importance at the farm level.There is still a need to determine whether certain parasites cause significant reductions andeconomic losses in animal or crop production {146}, and whether control strategies are reallyneeded {142}.

Current research for control strategies mainly focuses on selecting and breeding for host plantresistance {113, 114, 115, 147, 148}. As tropical pasture plants have been selected for only ashort time, vast sources of genetic variation still exist in their centers of diversity where plantshave been associated with endemic parasites over a long period. This natural variation shouldbe used first for germplasm screening and multilocational selection instead of initiating costlybreeding programs {113}.

An increased use of resistant varieties may lead to selection of highly virulent pathogenicraces and the breakdown of (single-gene based) resistance {113, 114}. To ensure durability,resistance should be combined with biological and cultural methods (e.g., burning, grazing,cutting, tillage, rotation etc.) in integrated pest management (IPM) programs. Biologicalcontrol of pests and diseases of forage plants is still largely unexplored {113}, except foreconomically important species such as the Leucaena psyllid, Heteropsylla cubana {138}.Further research will be needed to identify beneficial organisms and natural enemies ofpasture pests and to develop complex IPM strategies.

Chapter 4: Tropical pastures within regional and global ecosystems20

4 Tropical pastures within regional and global ecosystems

4.1 HydrologyInputs of water through rainfall and irrigation, its storage in the soil, and the outputs (runoff,evapotranspiration, deep drainage and groundwater recharge) are elements of the hydrologicalcycle that have to be in balance for an ecosystem to be stable and sustainable {56}. Bychanging a virgin landscape for the purpose of crop production and pastoral utilization,agriculture contributes not only to alteration in the flux of water, but also to changes in waterquality:

Large-scale deforestation is supposed to result in regional climatic and hydrological changes{149, 150, 151, 152}. For example, about half of the precipitation in the entire Amazon basinseems to result from water recycled by transpiration. Extensive deforestation would beexpected to greatly reduce the transpired water available for rainfall {151}. In Venezuela ithas been observed that deforestation of the southern slopes of the coastal Cordillera and north-easternmost Andean spur has led to loss of water retention capacity and to more rapid runoff.Streams draining this region, which formerly were year-round flowing across the Llanos, nowdry up during the dry season {151}.

Land and stream salinization has occurred in several semi-arid and arid regions of the world{153} as a result of clearing the native vegetation for agricultural development. Clearing offorests and woodlands for crops and pastures usually results in less water use andevapotranspiration by the replacement vegetation. Thus, more water must either run offincreasing the likelihood of erosion or move through the soil profile past the root zone {62}.This deep-drainage water enters the regional groundwater system and causes the watertable torise. Salts (principally NaCl) in the soil profile are dissolved and accumulate at lower points inthe landscape following evaporation or ultimately get into the streams {56, 62, 154, 155}. InWestern Australia, only 48 % of the divertible surface water resources remain fresh (less than500 mg total soluble salts per liter), and some 440 000 ha of once productive farmland havebecome salinisized {56, 154}.

Moreover, it is well known that excessive livestock pressure is upsetting the normalhydrological functioning of a landscape by decreasing infiltration and thereby increasingrunoff, as already mentioned in section 3.3. Especially in mountain ecosystems, the negativeeffects of hillslope denudation and high stocking rates become evident in flash floods andincreased sediment load in the draining rivers {150}. The increased suspended-sedimentconcentration debases water quality; the deposited sediments might block irrigation channels,generate severe flooding from raised riverbeds, fill reservoirs {156}, and might even lower theoperational efficiency and lifespan of hydroelectric plants {157}.

Hydrology 21

In addition, deforestation implies a reduction of shade. This can increase the temperature ofrunoff water, which directly affects the dissolved oxygen content that is essential for theaquatic fauna in draining rivers {86}. Lower pH values in surface waters might be related tothe organic deposits from cattle and the decomposition of organic sediments {86}.

Overfertilization of pasture land is another important factor which can have dramaticenvironmental and ecological impact such as accelerated eutrophication of surface waters: Forexample in 1986, one of the largest algal blooms ever documented appeared in LakeOkeechobee, a large, natural fresh-water lake in Florida, United States. When the algae begandying after completing their growth cycle, the resulting low dissolved O2 levels and high NH3

concentrations killed virtually all invertebrate life in the lake. Phosphorus was considered tobe the major factor causing eutrophication of Lake Okeechobee. An important source of P inthis special case was runoff of soluble P fertilizer applied to bahiagrass pastures (Paspalumnotatum) {158}. Leaching of nitrate as a result of incomplete cycling of symbiotically fixed Nunder legume pastures or high inputs of ammonium fertilizers, contributes to thecontamination of ground and drinking water, too {54, 56, 58}.

Most of the aforementioned hydrological changes that cause environmental problems are dueto mismanagement of natural resources. Several studies have been carried out to resolve suchproblems and to find land use and grazing systems that, as far as hydrological aspects areconcerned, are more sustainable:

With regard to salinization there would be less problems if the replacement vegetation usedwater in the same manner as the original vegetation {56}. Brigalow (Acacia harpophylla)forest is the original vegetation on approximately 8 million ha in north-eastern Australia.Much of the area has been developed for crop and pasture production. This development,together with the inherent salinity of the subsoil of much of the brigalow lands, has raisedfears about the potential for widespread dryland salting in these areas. To tackle this problema study was conducted assessing the effect of clearing brigalow forest on ground waterrecharge {159}. It was observed that no significant recharge occurred during the period inwhich crops and pastures were fully established. As brigalow is a shallow-rooted tree speciesand able to regulate transpiration in dry periods, the maximum depth to which water wasextracted from the soil and the resultant soil water deficits under brigalow forest were similarto those under crop and pasture. These results suggest that under average climatic conditionsof the region dryland salinity will not occur when these soils are developed for pastureproduction or opportunity cropping {159}. On the other hand, when removing deep-rootedtrees and woody plants (e.g., eucalypt, pine) an ecological niche is created which should befilled up by deep-rooted species {160}.

To control salinization various reforestation strategies have been tested such as strip planting,valley planting, extensive reforestation and agroforestry. Agroforestry has a great potential to


lower saline groundwater tables, though high-density reforestation over a large proportion ofthe cleared area seems to be the best strategy when rapid and large groundwater levelreductions are required {153, 154, 155, 161, 162}.

Concerning nutrient losses due to runoff and leaching, which might cause eutrophication ofsurface waters, there is an urgent need to reconsider current fertilizer application levels. Afield study conducted on a bahiagrass pasture in Florida revealed that it is possible to reducethe P application rate by 50 % (from 48 kg to 24 kg P/ha) without significantly altering growthor quality of bahiagrass {158}. Grasses that form an intimate mixture with legumes inpastures, have the advantage of readily taking up N and thus minimizing loss of nitratethrough leaching {163}.

Erosion control measures are indispensable to reduce the sediment load of rivers and thus toimprove water quality. The potential contribution of pasture and forage plants to this issue isdiscussed in section 3.3.

The way in which a production system interacts with the hydrological cycle, and theimplications of these interactions regarding the longer-term stability and sustainability areoften disregarded. To understand the hydrological consequences of land use changes anddeforestation it is necessary to appreciate the fate of deep drainage, salt and nutrientdistributions, and the complex patterns of surface and groundwater movement. At the momentthere is a lack of standard methodology for assessing the local, regional and globalhydrological consequences of extensive forest clearing and land use changes. There is anobvious need for reliable models that describe hydrological processes if sustainable land usesystems are to be developed {56}.

4.2 Regeneration of degraded landAs a result of overgrazing, deforestation, inappropriate cultivation techniques, miningactivities, and other anthropogenic disturbances, large areas are today in an advanced stage ofdegradation. Land degradation affects three-quarters of the world's grazing land, half of therainfed cropland, and a quarter of the irrigated land {164}. Some characteristic problems thatare encountered in the course of degradation and desertification of ecosystems are loss ordisturbance of vegetation cover, increase in soil erosion, loss of available nutrients andorganic matter, soil acidity with high levels of toxic manganese or aluminum, salinization andscarcity of microbial activity {165}.

In view of population growth and the increasing demand for agriculturally productive land,strategies to restore the productivity of abandoned sites are of major importance and mighthelp to reduce the pressure on still-productive ecosystems {156, 166}. Regeneration mayrange from restoration of a degraded ecosystem to the original ecosystem, from reclamation of

Regeneration of degraded land 23

a desertified ecosystem to an ecosystem similar to that of the original situation by usingpreexisting species, or to rehabilitation of a desertified ecosystem by planting exotic species{135, 167, 168}.

The prospect of establishing forage plant species which at the same time improve soilchemical, physical and biological properties of a degraded area, often encourages thebeginning of revegetation efforts in the tropics {109, 156, 169, 170, 171}. Input-intensivetechniques to reclaim degraded pastures, such as mechanization and application of fertilizersand lime, have been employed in many Amazon countries, especially in the BrazilianAmazon. The vigorous forage grass Brachiaria humidicola which is well adapted to poor acidsoils, has been used to replace degraded Panicum maximum and Hyparrhenia rufa pastures{74, 166, 172}. From a technical perspective, high-input technology can be effective inrecuperating (pasture) ecosystems. However, the intensification of land use implies thedisadvantage that it is expensive due to reliance on machinery and fertilizers {74, 172}.

An alternative to the above approach is a low-input soil management technology which isbased mainly on the use of plants adapted to soil constraints rather than elimination of all soilconstraints to meet the plants' requirements {2, 74}. Plants suitable for revegetation should beadapted to nutrient deficiency, should be easy and rapid to establish, should persist and beresistant to prevailing pests and diseases {143}.

On impoverished sites with a poorly developed nitrogen cycle, legumes efficient in N2

fixation can be sown as early colonizers and as a 'nurse crop' facilitating the establishment ofother species {168}. Today, much effort is made to select plant species and genotypes adaptedto a wide range of unfavorable ecological conditions {2, 143, 169, 170, 171, 173}.

Plant establishment in acid or desertified ecosystems is often limited due to inadequate Pnutrition, especially in the case of legumes which require relatively high levels of P for N2

fixation. Also the absence of symbiotic microbes such as vesicular-arbuscular mycorrhizal(VAM) fungi, which are of particular importance for the absorption of nutrients of lowmobility in soil solution (P, Zn, Cu), can severely limit seedling establishment, plant growth,and plant survival {165, 174}. In the case of degraded and eroded soils that have lowconcentrations of VAM propagules, VAM inoculation is likely to increase plant performance,establishment and drought tolerance {175, 176}. Also biological N2 fixation may be improvedby selecting highly effective rhizobium strains. Thus, appropriate microsymbiont managementcould be a tool to promote revegetation, but the practical and cost-efficient utilization of thistechnology will still require more research {2, 143, 176}.

Including woody plants in regeneration programs is of special importance to control salinity(section 4.1), reduce wind speed (section 3.3), and improve microclimatic conditions (section3.4) {109, 111, 168}. Moreover, island-forming trees may provide attractive habitats for seed


carrying birds and thereby enhance the quantity and diversity of animal-dispersed plantspecies recruited in the surrounding area {166, 177, 178}.

Seed application methods for extensive revegetation approaches (e.g., aerial seeding) may beless successful unless good seed-soil contact is ensured {179}. The use of livestock as agentsof seed dispersal may be an interesting alternative. Livestock could be strategically fed withseeds of desirable species to disseminate them into areas targeted for improvement. The moist,nutrient-rich dung may facilitate seed germination and plant establishment. Further studieswill be necessary to test this approach and to find further inexpensive methods of seedapplication for revegetation {177, 179}.

The success of revegetation efforts depends, apart from abiotic factors, substantially on bioticinteractions that affect plant establishment. Interactions within and between plant species aswell as plant-animal interactions need to be considered {168, 177}.

The utilization of species mixtures and the development of diverse plant communities ispotentially important for stability of vegetation cover and productivity. Regeneration ofdegraded land should not depend upon only one single species. However, research is neededto investigate if species sown in mixtures are compatible and if successful coexistence ispossible {168}.

With regard to animals affecting plant establishment and persistence on regenerated land,more attention should be directed to pollinating insects {180}, seed dispersal, below-groundherbivory and grainivory. Seed predation is potentially a major factor contributing to thefailure of regeneration. Especially rodents and ants have been shown to be primary seedpredators. They can decrease seed reserves in annual grasslands and desert annualcommunities by 30-80 % {136, 177}.

Grasses, legumes and woody forage plants, e.g., in silvopastoral systems, have a greatpotential to play a major role in the revegetation of degraded land, in salinity control, erosioncontrol, sand dune stabilization, shelterbelt establishment and rehabilitation of mined areas{178, 181}. However, besides the selection of species adapted to edaphic and climaticconstraints, an understanding of the interactions between plants, animals, and microbes iscrucial for the success of regeneration efforts.

4.3 BiodiversityBiological diversity (= biodiversity) is the variety of life and its processes, including thevariety of living organisms, the genetic differences among them, the communities, ecosystemsand landscapes in which they occur, plus interactions of these components. In view of globalenvironmental changes and accelerated extinction of species, biodiversity is more and morecapturing public and scientific attention {182, 183, 184, 185, 186}. There are several reasons

Biodiversity 25

for preserving the world's variety of life, such as the moral obligation to protect organisms,aesthetic reasons, the need to prevent genetic erosion for ensuring the evolutionary potentialof our crops and pastures, and last but not least the maintenance of ecosystem functions. Lossof biodiversity may negatively influence the stability of ecosystems {187} as well as thequality and quantity of ecosystem services, such as maintenance of soil fertility, nutrientcycling, natural control of pest organisms, amelioration of climates, etc. {188, 189}.

It is estimated that a quarter of the world's biodiversity may be under serious threat ofextinction over the next 20-30 years (15,000 to 50,000 species/year) {190}, and there is nodoubt that rates of extinction greatly exceed rates of evolution of new species {188}.Especially those species, which require non-developed areas and stable conditions, areendangered whereas short-lived species with rapid growth rates are favored by cultivation andthus have increased in abundance {182}. Some of the main factors that affect speciescomposition and diversity are large-scale changes in land use patterns and the introduction ofnew agricultural technologies (e.g., fertilizers, pesticides, irrigation, replacement of locallyadapted varieties, etc.).

The role of grazing and pasture management in this context is rather complex:

Deforestation in tropical countries has dramatically accelerated during the last decade,increasing from 11 million hectares per year to nearly 20 million {191}. The loss of species asa result of deforestation and degradation of tropical forest land is widely discussed {183, 188,191, 192}. In the Amazon basin, at least 10 million hectares of forest have been converted tohighly unstable pastures, of which about 50 % were in advanced stages of degradation in 1990{74}. Therefore, one of the main objectives of today's pastoral research is to increase thelongevity of still-productive pastures and to reclaim degraded land in order to reduce the rateof forest clearing {74, 143, 172, 193}. Genetic erosion is being curtailed by germplasmcollection and preservation. This collection is the basis for the identification and developmentof adapted forage species, suited to different environments and agricultural practices {114,143, 161}.

Ecosystem dynamics that determine the composition of vegetation on rangelands are rathercomplex and are triggered by natural mechanisms (e.g., weather, fire, competition,allelopathy, shading) and by management actions (stocking rate, burning, introduction ofexotic plants, fertilization, irrigation, etc.) {194, 195}. Increasing resource availability, e.g.,through fertilizer application or irrigation, typically increases yield, but at the same time mayreduce species diversity. This relationship between production and diversity is inverse becausecompetitive plants are often better able to capitalize on increased resource availability and cantherefore increase their biomass or density at the expense of slower-growing, stress-adaptedspecies {91, 168, 187, 196}.


High stocking rates in the tropics frequently lead to overgrazing with subsequent degradationand decline in biodiversity. In environments with pronouncedly seasonal rainfall, perennialgrasslands can be converted to annual grasslands by grazing {91, 195}. Livestock is alsolikely to select more palatable species to such an extent that eventually unpalatable plantspredominate {98, 112, 194, 195, 197, 198}.

Concerning the effects of herbivores on plant growth and reproduction there are two majoropposing views: On the one hand, herbivory is suggested to be detrimental to plants {199,200, 201}, representing a selective pressure for the evolution of plant defenses. On the otherhand, plants have been shown to benefit from being grazed, as their seeds may be distributedin the dung, and grazing may stimulate the production of flowers, herbage and roots,ultimately causing greater fitness {98, 177, 196, 199, 201, 202}. The extent of compensatorygrowth is influenced by external factors, e.g., competition with neighbor plants, nutrientavailability and timing of herbivory {203}.

Selection pressure resulting from grazing in combination with a semiarid climate is animportant force that through evolutionary periods has influenced the present structure ofnatural grasslands and their relative ability to withstand grazing: In semiarid environments,basal meristems, short stature, high shoot density, rapid regrowth following defoliation, andspreading by rhizomes and stolons constitute adaptations that enhance survival and maypromote tolerance or avoidance of grazing. Many grazing-tolerant grasses have totally co-evolved with large herbivores. On the other hand, in subhumid areas tall grasses without thecapacity of spreading by rhizomes and stolons predominate. Tall growth forms are adaptationsthat enhance the grasses' competitiveness for light but make them more vulnerable to grazing.In communities of such grazing-intolerant species, grazing usually increases diversity ofplants by decreasing the ability of dominant species to competitively exclude others, and bycreating gaps, freeing resources such as light and nutrients. In contrast, in semiarid grasslandswith a strong evolutionary history of grazing, moderate herbivory appears to have a relativesmall effect on community composition {204}.

Today, there is much interest in using exotic species for pasture improvement {205}. Suchpastures may be very productive initially, but often productivity declines in the long run due tochanges in nutrient availability and reduced competition, leading to the invasion ofundesirable weeds and native grasses {20, 74, 160, 172}.

Reversely, introduced fodder plants can develop a weed potential {160, 206}: Between 1947and 1985, 463 exotic grass and legume species, represented by at least 2033 accessions, wereintentionally introduced into northern Australia. Of these, 60 species (13 %) became listed asweeds: 21 were weeds of cropping, 20 were weeds of conservation and 19 were weeds of bothsectors {206}. There is much concern that biodiversity in natural areas might be threatened bythe introduction of exotic species eventually killing or competing with native species {183,

Atmosphere and global warming 27

192} which could be essential components of balanced, co-evolved ecosystems. On the otherhand, some authors claim that paleo-ecological and historical data show that species havecontinuously been added or removed from ecosystems, changing species composition andstructure, but these exotics have rarely affected ecosystem functions {207}. However, theconsideration of weed potential and competitiveness must be an integral part of current andfuture evaluation programs for selection of new pasture species {161, 192}.

Moreover, disturbances such as fire and diseases can greatly affect biodiversity {166}.Removal of fuel and organic matter by grazing can be considered as a factor reducing theincidence of fire {98, 182}.

Farming practices, grazing and changes in vegetative cover also influence the variety andabundance of the fauna {69, 98, 182, 198}. Tropical grasslands can harbor a rich communityof above-ground insects {208} and of earthworms. In pastures established in formerly forestedareas, species diversity of earthworms seems to be lower. Much depends on (i) the adaptivepotentialities of the former forest species to take advantage of the new environment, and (ii)on the possibility for pantropical species to invade these new habitats {72, 82}. Similarly,introduced collembola prevailed in pastures where exotic plant species occur, whereas nativecollembola were predominantly restricted to natural pastures {69}. Increased grazing by sheepdecreased species richness and increased uniformity of collembola in both pasture types {69}.

On the other hand, structural diversification and patchiness of landscapes may increase speciesrichness. For instance, the presence of agricultural fields within unfarmed areas has beenobserved to increase the regional diversity of birds {209}. Appropriate grazing managementcan be a tool in regulating the types and quality of bird habitats {198}.

Preservation of species, genotypes, communities and ecosystems should not only be realizedby creating wildlife reserves and parks. We must also learn to use land in a sustainable wayand to manage pastures in such a manner that most of the biodiversity is retained {20, 183,192, 210, 211}. Research is needed to identify keystone species and functional groups, whichare important to maintain all ecosystem processes that are essential for sustainability {182,183, 186, 192, 212}.

4.4 Atmosphere and global warmingChanges in the chemical composition of the earth's atmosphere which possibly lead to globaland regional climatic changes have caused increasing concern during recent years. Thesechanges seem to be related to activities of man such as energy consumption. Production anduse of chemicals in the industrialized countries are probably far more significant than globalagricultural production. The contribution of the latter to global warming has been roughlyestimated to be 15-25 % {213}.


The major processes related to agriculture causing atmospheric changes are:

• Deforestation and biomass burning, causing net release of CO2, CO and other relevant tracegases such as nitrous oxide (N2O), ozone (O3) and methane (CH4) {214, 215, 216, 217,218, 219, 220, 221, 222, 223};

• energy from fossil fuels used for fertilizer production (mainly nitrogen fertilizers) andmachinery causes net CO2 release {224};

• use of nitrogen fertilizers can enhance N2O-release {84, 214, 217};

• soil degradation and destruction of organic matter produce net CO2 release {213, 218, 224,225};

• methane (CH4) is released in paddy rice cultivation and by ruminants {214, 222, 226, 227,228, 229, 230, 231, 232}.

The significance of pastoral activities in this context is rather complex:

When replacing native rainforest ecosystems in large areas, pastures tend to contribute toglobal warming in several ways {214}. Carbon stored in the forest biomass will be released byclearing, and although productive pastures can theoretically assimilate as much carbon asmature rainforest, many pastures in rainforest areas (especially in South America) haveundergone a rapid process of degradation within less than 10 years, leaving extended areas ofunproductive land {218}. Thus, forest clearing for pasture establishment leads to net CO2

release due to biomass burning or decomposition, if pastures are not maintained productive byusing external inputs and appropriate management. Furthermore, biomass burning increasesconcentrations of CO, NOx and ozone in the surface-near atmospheric layer, NOx being animportant precursor of ozone, which apart from being toxic to plants also contributes to thegreenhouse effect. Recent research has revealed that rainforest seems to be a globallyimportant sink for ozone; thus rainforest clearing destroys at the same time the sink as moreozone and ozone precursors are produced {214, 215, 220}. Pastures could also produce moreN2O than the native forest, particularly when nitrogen fertilizers are used {84, 214, 217}.Increased cattle population would produce more methane {214, 226, 227, 228, 230, 231}.

Consequently, in view of global warming, replacement of native rainforest by pastures doesnot seem to be a desirable option (as well as from other points of view, see sections 4.1 and4.3).

On the other hand, cultivation of improved pastures and forages can also counteract thecurrent processes of climatic change. There are, for instance, indications that deep-rootedgrasses store large amounts of organic carbon in the soil, and may therefore play a vital part instabilizing the global cycle and minimizing the greenhouse effect of atmospheric CO2 {233}.

Atmosphere and global warming 29

The carbon stored worldwide in soil organic matter exceeds the amount retained in biomass{213}. Agricultural techniques which increase soil organic matter content can, therefore,create an important CO2 sink. The role of fodder plants in integrated farming systems forrestoration of soil organic matter content is well known (see section 3.1.1) as is thecontribution of improved fallows, alley cropping and agroforestry systems. Pasture species canalso be used for revegetation of degraded lands (section 4.2).

Of particular importance is the fact that legumes, when providing subsequent crops (orcompanion grasses in pastures) with biologically fixed nitrogen and by these means replacingmineral nitrogen fertilizer, can considerably reduce the consumption of fossil energy inintensive agricultural systems. It has been shown that nitrogen fertilizer use in average farmsin Germany accounts for about 50 % of fossil energy consumed for plant production {224}.Strategies for reduction of atmospheric CO2 are particularly efficient, if not only sinks forexcessive CO2 release from fossil sources are created, but if at the same time the use of thelatter is substituted by solar energy assimilated by plants. This fact has been observed forforestry CO2 strategies {219}, but would also be true for the case of biological N2 fixation.

Little seems to be known about the amount of N2O released from tropical soils. In somepublications, the use of nitrogen fertilizer is reported to enhance the production of thisgreenhouse gas which occurs as an intermediate during denitrification, but there seem to be nopublications about the amounts of nitrogen fixed by pasture legumes undergoing the sameprocess. This is an area in need for further research.

Methane production by ruminants, particularly cattle, has been a matter of interest for manyyears, because of the nutritional energy loss involved. Methane is the second importantgreenhouse gas after CO2. According to recent estimates, worldwide animal husbandryaccounts for about 20 % of global methane production and contributes with about 4 % to thewhole problem of global warming {231}. Methane emissions during rumen fermentationdepend on diet composition and level of feeding {226, 227, 228, 229, 230, 231}. In general,methane release per unit animal product (milk, meat etc.) decreases with higher individualanimal performance, so that some authors suggest that all measures improving individual milkand beef yields would be vital to control the methane problem. These measures includesupplementation with urea, minerals, and high quality feed (sugar, proteins, starch, fat),chemical control of rumen microflora, chemical manipulation of volatile fatty acid formationin the rumen, etc. {227, 228}. Nevertheless, methane production is not the only point to beconsidered in order to determine ecologically adequate feeding levels and diet compositionsfor ruminants.

Energy requirements per kg milk produced decrease significantly if milk yield per cow isincreased from 2000 to 5000 kg/year, but less for further increase to 8000 kg/year {234}. Atthis high level of performance, forage intake has to be progressively replaced by concentrates,


generally produced with fossil fuel inputs. Furthermore, a protein surplus is unavoidable indiets for very high production levels {83, 234}, creating new problems regarding nitrogenlosses to groundwater and atmosphere. Medium feeding levels based on good-quality greenfodder seem to be optimal from both the environmental and animal health point of view.Tropical pasture plants can probably significantly help to reduce methane emissions fromcattle fed on low-quality roughage by increasing forage intake, digestibility, turnover in therumen and individual animal performance, as reported in numerous publications. However,investigations about the benefits of tropical pasture legumes for animal production have so farnot been evaluated with regard to global warming concerns.

In addition to affecting global climate, it is expected that an enriched CO2 atmosphere willinfluence biotic interactions because of the critical role of CO2 in photosynthesis. There areindications that plants may respond to enriched CO2 environments by increasing growth andwater use efficiency, whereas foliar nitrogen concentrations may decline {235}. The effects ofsuch responses on plant-plant as well as plant-animal interactions are still poorly understood.

Conclusions 31

5 ConclusionsThe degradation of natural resources in terms of soil fertility decline, erosion, desertification,species extinction and disturbance of the hydrological cycle through pastoral mismanagement,are testimony to the fact that current land use systems in tropical regions are often far frombeing sustainable. Up to the present time, scientists have not been successful in developingsound guidelines for the development and management of sustainable pastoral systems, asemphasis of most research activities has been put on improving short-term productivity. Theway in which the farming system interacts with biotic and abiotic elements of the ecosystemand the implications of these interactions for the long-term stability has usually been neglectedor has been studied apart from the farming system and without drawing conclusions withregard to management practices. However, critics of cattle husbandry would do well to notethe importance of cattle referring to socio-economic aspects and human nutrition, andreconsider the role of cattle and pasture plants within diversified mixed farming systems.

Possible strategies towards the solution of the problem of grazing-induced land degradationare:

1) Increasing the longevity and stability of still productive pastures and arable land in order toavoid further deforestation and expansion of agriculture into intact natural landscapes;

2) restoring productivity of degraded pastures and abandoned land.

Progress towards sustainable pasture and land use systems will only be made if theimplications of agricultural practices are studied in an integrative way and if they areunderstood as parts of the regional ecosystem.

The present literature review indicates that basic data on ecological effects of pastureestablishment and livestock production are still scarce, especially in the case of long-termeffects at the regional and global level, e.g.:

• Little is known about the contribution of tropical legumes to soil acidification and aboutthe effects of pasture species on soil biology;

• future management research should include studies of the hydrological consequences ofland use changes for pastoral purposes, and should consider the effects on water quality;

• biotic interactions and relationships between plants, animals and microbes need to beidentified to enhance the probability that species will co-exist and thereby facilitate greaterspecies diversity on a given site;

• a major research challenge is to identify keystone species and functional groups to sustainecosystem processes;

Chapter 5: Conclusions32

• pastoral research should address the question as to how create a CO2 sink to stabilize theglobal carbon cycle, e.g., by cultivation of deep-rooted species and by increasing soil OMcontent;

• methane emissions from cattle should be reduced by improving forage quality.

Technologies of pasture plant uses for other purposes than feeding livestock, e.g., for soilimprovement or revegetation, still lack tropical experience to a large extent and are far frombeing fully developed. Future pastoral research should improve knowledge on themultipurpose potential of herbaceous and woody forage species. Researchable priority topicsare, among others:

• The potential of pasture species to improve infiltration rates and water retention capacity,and to produce rougher surfaces for erosion control;

• selection of pasture species adapted to unfavorable edaphic and climatic conditions forrestoration of degraded land;

• quantification of nutrient fluxes in integrated cropping systems and generation of furtherinformation on the spatial and temporal variation in recycling processes;

• further exploration of the potential of pasture plants for management of phytosanitaryproblems, including research on beneficial organisms and natural enemies in pastureecosystems, and on IPM strategies to control pests and diseases of valuable pasture plants;

• influence of multipurpose trees and forage plants on microclimate.

Research topics should be addressed within multilocational research programs for a widerange of ecological and socio-economic conditions. It is important that techniques, which arefeasible and socially acceptable to smallholders in the tropics, are put into practice as soon aspossible if environmental degradation is to be halted or at least to be slowed down.Interdisciplinary research and interinstitutional collaboration will be indispensable to achievethe goal of successful development and implementation of sustainable land use systems.

References 33

6 References

1

Mulongoy, K. and Kang, B.T. (1986): The role and potential of forage legumes in alleycropping, live mulch and rotation systems in humid and subhumid tropical Africa. In: Haque,I., Jutzi, S. and Neate, P.J.H. (eds.), Potentials of forage legumes in farming systems of sub-Saharan Africa. Proceedings of a workshop held at ILCA, Addis Ababa, Ethiopia, 16-19September 1985. Addis Ababa, Ethiopia: ILCA (International Livestock Centre for Africa), p.212-231.

Keywords: legumes; alley cropping; live mulch; mulch; Africa; Leucaena leucocephala; weedcontrol; maize; yields; nitrogen fixation; nematodes; pest control; improved fallow; erosion;weeds.

Abstract. Fragile, low activity clay soils, which are prone to erosion and are characterised byinherently low fertility, are common in humid and subhumid tropical Africa. On these soils,forage legumes play an important role in developing sustainable and low input cropproduction systems. Woody and herbaceous species such as Leucaena leucocephala,Gliricidia sepium, Flemingia congesta and Sesbania rostrata have shown good potential forinclusion in alley cropping systems. Mucuna pruriens var. utilis is one of the most promisingsources of in situ mulch in small- and large-scale crop production. Live mulches ofPsophocarpus palustris and Centrosema pubescens smother weeds effectively and have beenshown to sustain high maize yields with little fertilizer N input. Despite the encouragingresults obtained with forage legumes on less acid soils, further research is needed to selectspecies that can be included in low-input crop production systems on strongly acid soils.

2

Sanchez, P.A. and Salinas, J.G. (1981): Low-input technology for managing Oxisols andUltisols in tropical America. Advances in Agronomy 34:279-399.

Keywords: Oxisols; Ultisols; South America; low-input technology; tropics; fertilizers;sustainability; adapted germplasm; soil chemical properties; phosphorus; nitrogen fixation;soil acidity.

Abstract. Low-input technology for acid soils of the tropics can be defined as a group ofpractices that can produce about 80% maximum yields of acid-tolerant plant species andvarieties with the most efficient use of soils and chemical inputs. The term "low" is used inrelation to "high"-input technology where the application of fertilizers and amendmentslargely eliminate chemical soil constraints. The identification of plant species and ecotypestolerant to the main acid soil stresses allows the development of low-input soil managementsystems for Oxisol-Ultisol regions where socioeconomic constraints prevent the widespreadapplication of large quantities of lime and fertilizers. The basic approach is to use plantsadapted to acid soil constraints, to maximize the use of fertilizers and lime needed to produceabout 80% of their maximum yield, and to take advantage of favourable attributes of acid,infertile Oxisols and Ultisols. Several technology components are reasonably well identifiedand could be used as building blocks for specific management systems.

Chapter 6: References34

3

Fearnside, P.M. (1980): The effects of cattle pasture on soil fertility in the Brazilian Amazon:Consequences for beef production sustainability. Tropical Ecology 21:125-137.

Keywords: sustainability; cattle; Amazon region; soil chemical properties; degradation.

Abstract. Amazon rainforest is fast being replaced by cattle pastures as investors respond tofinancial incentives and the lure of the new highways. The Brazilian government'sencouragement of pasture is linked to claims that pasture improves soil fertility and thereforerepresents a "rational" means of development in the Amazon. A review of information relatedto the ongoing debate concerning soil fertility changes under pastures casts doubt both on theclaims of improved fertility for pasture growth, and on the presumption of indefinitelysustainable yields of beef cattle.

4

Atta-Krah, A.N. (1990): Alley farming with Leucaena: Effect of short grazed fallows on soilfertility and crop yields. Experimental Agriculture 26:1-10.

Keywords: improved fallow; yields; sustainability; legume trees; maize; alley cropping;Leucaena leucocephala; soil chemical properties.

Abstract. A long-term trial with Leucaena leucocephala was initiated in 1982 to test thesustainability of Leucaena-based alley farming compared to a conventional cropping systemwithout trees and with continuous cultivation of maize. It assessed the integration of shortgrazed fallows in rotation within Leucaena alleys and their effect on soil fertility and cropyields. The various treatments had no effect on soil pH during the four-year period of the trial.The organic carbon and total nitrogen contents of the soils under conventional cropping werelower by the end of the fourth year than those under alley cropping and alley grazingtreatments, whereas soil phosphorus levels were lower in the alley cropping and grazing plots.Foliage dry matter production of Leucaena under alley cropping management ranged from 6.0to 6.7 t ha-1 a-1 under continuous cropping and reached 8 t ha-1 when alley cropping waspreceded by a grazed fallow. Crop yields were consistently higher with alley cropping thanwith conventional cropping. Alley cropping plots in rotation with two year grazed fallowsgave significantly higher crop yields during cropping years than those under continuouscultivation.

5

Gichuru, M.P. (1991): Residual effects of natural bush, Cajanus cajan and Tephrosiacandida on the productivity of an acid soil in southeastern Nigeria. Developments in Plant andSoil Science 45:417-422.

Keywords: Cajanus cajan; intercropping; improved fallow; Tephrosia candida; legumes;nutrient cycle; Nigeria; shrubs; maize; yields; cassava; West Africa; soil chemical properties;nitrogen fixation.

Abstract. An experiment was established in 1986 to examine the contribution of Tephrosiacandida and Cajanus cajan shrubs to improving the productivity of an acid soil. The maintreatments were N levels (0 and 60 kg per ha) with subplots of maize/natural bush,maize/Tephrosia candida, maize/Cajanus cajan, maize + cassava/natural bush, maize +

References 35

cassava/Tephrosia candida, and maize + cassava/Cajanus cajan. In 1988, all plots werecleared and maize uniformly planted to study the residual effects of the treatments. Noresidual effects of N application were observed. Tephrosia candida and Cajanus cajanincreased surface soil organic carbon and total N levels over the natural bush. However, onlyTephrosia candida plots produced improved maize grain and stover yield. Highly significantcorrelations were found between maize grain yield and earleaf N (r = 0.73), grain N (r = 0.51),and stover N (r = 0.54) contents. These results suggest that Tephrosia candida increased Navailability in the soil. Therefore, the shrub has potential for improving the productivity ofacid soils under traditional systems, where N is limiting due to the absence of N2-fixinglegumes in the natural bush fallow.

6

Hussein, S.E.G. (1990): The influence of fallow under Acacia senegal (L.) Willd. on the Cand N content of the soil. Beiträge zur Tropischen Landwirtschaft und Veterinärmedizin28:217-222.

Keywords: natural fallow; shifting cultivation; soil chemical properties; legume trees; tropicalsavanna; Africa; fallow.

Abstract. The paper describes the origin, properties and utilization of the Goz sands. The soilis generally utilized in a shifting cultivation system: cultivation for 4 years, 12 to 15 years ofbush fallow under Acacia senegal (L.) Willd. A comparative investigation of soil profilesexhibited a considerable accumulation of organic soil matter and nitrogen under fallowvegetation.

7

Prinz, D. (1986): Increasing the productivity of smallholder farming systems by introductionof planted fallows. Plant Research and Development 2:31-56.

Keywords: farming systems; legumes; improved fallow; soil chemical properties; yields;nutrient cycle; live mulch; mulch; alley cropping; ley farming; legume trees.

Abstract. The doubling of the population in the developing countries which is expected overthe next 25 years makes it necessary, assuming that the same amount of land is available forcultivation, for productivity per unit land area to be at least doubled. Of the many possiblemethods offered by tropical crop science we have selected one, planted fallow, and havebriefly described its potential in relation to peasant farming systems. Planted fallow is thetargeted use of plant species in order to achieve one or more of the aims of bush fallow withina shorter time or on a smaller area. Two main forms can be distinguished: successive andsimultaneous fallow, and two sub-forms: ley farming and multi-storey cropping. Apart fromgrasses, legumes are the plants chiefly involved in systems of planted fallow. A stableproduction system can be built up and an increase in area productivity achieved by using oneor several forms of improved fallow combined. But if yields per hectare are to be doubled allthe elements of "integrated plant nutrition" available will have to be used.


8

Nicholaides, J.J., Bandy, D.E., Sanchez, P.A., Benites, J.R., Villachica, J.H., Coutu, A.J.and Valverde, C.S. (1985): Agricultural alternatives for the Amazon Basin. BioScience35:279-285.

Keywords: soil chemical properties; shifting cultivation; annual field crops; Peru; tropicalforest; pastures; deforestation; Amazon region; fertilization; crop rotation; seeds; agroforestry;rice.

Abstract. As population pressure increases, shifting cultivation practices are considered to beone reason for deforestation in the rainforest areas of the Amazon basin. As an alternative, atechnology for continuous cultivation using rotations of annual food crops such as rice-peanut-soybean, has been developed in Yurimaguas/Peru. The effects of this new technology,using improved seeds, fertilizers, lime, insecticides, plant-spacing and weeding techniques onsoil properties, farmer acceptance and economic feasibility were examined. Other alternativesto shifting cultivation could be legume-grass pastures or agroforestry on sloping soils, andpaddy rice on alluvial soils. Limitations and potentials for these improved technologies arediscussed. (Abstract by bibliography authors)

9

Chheda, H.R., Babalola, O., Saleem, M.A.M. and Aken'ova, M.E. (1981): Sown grasslandas an alternative to shifting cultivation in lowland humid tropics. Proceedings of the XIVInternational Grassland Congress, Lexington (USA), p. 774-777.

Keywords: Cynodon; shifting cultivation; mixed farming; allelopathy; soil physical properties;soil chemical properties; erosion control; pest control.

Abstract. Agriculture based on existing forms of shifting cultivation will not be able tosupport and feed adequately the rapidly increasing human population of the lowland humidtropics of Africa. The forest and natural fallows have shortened and even disappeared in someareas because of rising food demands. Crop yields are low and continue to decline. What,then, are the alternatives? Using Cynodon as an example, an attempt is made to show thatmixed farming offers an alternative whereby the nutrient status and physical properties of thesoil can be maintained, erosion can be checked, weeds can be kept under control, and thebuildup of pests and parasites minimized or avoided. A synthesis of several years of intensivebreeding and agronomic research at the University of Ibadan indicates: 1. Availability ofimproved robust, nonrhizomatous Cynodon genotypes with an annual dry matter (DM) yieldpotential of around 15 tons (t)/ha, adequate for production of 650 kg/ha of live-weight gains ofthe local Zebu cattle when grazed from April to December. 2. Annual nutrient mobilization ofover 122, 25, 175, 37, and 29 kg/ha of N, P, K, Ca, and Mg, respectively, by Cynodonpastures. Around 20% of the nutrients mobilized are "pumped up" from soil layers below 30cm. 3. Possession by several Cynodon genotypes of high microbial population in therhizosphere, capable of fixing varying quantities of N. IBX-7, an improved hybrid, is able tofix up to 2 kg/ha of N/week. 4. Increase in soil organic matter under temporary Cynodonpastures, replenishing a high proportion of the substantial loss of 63% in organic matter (OM)under 10 years of continuous cultivation. 5. Improvement of soil physical properties underCynodon pastures as measured by soil aggregate size and aggregate stability, bulk density, andtotal porosity. 6. Protection against erosion with established Cynodon. Cynodon, when fullyestablished, gives almost as much protection against erosion as does forest with closed

References 37

canopy. On a soil with 3% slope, water runoff from Cynodon plots was 5.3% of the totalerosive rain of 155 cm. Soil losses under pasture during the growing season were less than10% of those observed in maize and cowpea plots. 7. Ability of root exudates collected fromseveral Cynodon improved genotypes, when placed with seeds of common tropical weedspecies, to inhibit germination or reduce seedling growth. Aqueous extracts of Cynodon rootsshowed similar inhibitory effects. The inhibition factor disappeared after 27 to 45 hours ofstorage. 8. Resistance of Cynodon genotypes to the root-not nematodes (Meloidogyne spp.).Growing of Cynodon in highly infested soils decreased the root-not nematode populationappreciable in 6 months and eliminated the nematodes completely within 18 months.Consequently, tomato yields increased by about 300%.

10

Bishop, J.P. (1982): Agroforestry systems for the humid tropics east of the Andes. In: Hecht,S.B. (ed.), Amazonia: Agriculture and land use research. Cali (Colombia): CIAT (CentroInternacional de Agricultura Tropical), p. 403-413.

Keywords: agroforestry; deforestation; degradation; Brachiaria humidicola; Desmodiumovali-folium; legume trees; swine; cattle.

Abstract. The author suggests agroforestry systems that integrate animal production,fuelwood/timber and food crop production for small farms of the humid lowlands east of theAndes. In this region, colonization, deforestation and unstable forms of land use have led toaccelerated soil degradation, weed/pest invasion and decreasing yields. Two examples ofagroforestry systems developed in the Ecuadorian Amazon region are presented as possiblesolutions of land degradation problems. After two years of food crop production, the foragelegume Desmodium ovalifolium is sown together with the root forage Canna edulis, a localbanana variety (Musa acuminata x M. balbisiana ABB) and the fast growing native legumetree Inga edulis. Forages and banana serve for swine raising, which is economically importantin the region, while legume trees improve soil fertility and provide fuelwood. The swine-fuelwood production represents a form of improved fallow within an 8-year rotation cycle andis considered to have a great potential to improve economic productivity and ecologicalstability of small farms. Another suggestion is the integrated cattle and timber production inorder to maintain long-term productivity of pastures. The forage grass Brachiaria humidicolais intercropped with the forage legume Desmodium ovalifolium and the timber tree Cordiaalliodora. Considering a 20-year period, the benefit from timber production could equal theincome from cattle raising, thus improving both economic and ecological conditions as wellas sociological viability of livestock production in the region. (Abstract by bibliographyauthors)

11

Humphreys, L.R. (1994): Tropical forages: their role in sustainable agriculture, LongmanScientific & Technical, Harlow, Essex, England, 414 p.

Keywords: sustainability; mixed farming; soil improvement; soil erosion; soil properties;trees; shrubs; pastures; intercropping; weeds; diseases; nutrient cycle.

Abstract. This comprehensive volume demonstrates how forages can sustain tropical croppingsystems and be used to combat the environmental problems of deteriorating soils anddeclining crop yields associated with monocropping and the development of marginal lands.


'Tropical forages' begins by examining the advantages of mixed farming with animals andcrops, which can improve soil structure and reduce soil erosion to enable more efficient use ofenvironmental resources and help protect crops from disease. This added flexibility in turnleads to the diversification and stabilisation of farm income. The book moves on to considerthe management of different cropping systems involving forages and the science on whichthey are based. These systems include: tree and plantation crops combined with pastures;shrub legumes grown with annual crops; ley systems in which pastures are rotated with annualcrops; and the intercropping of annual crops with forage legumes. The author emphasizes theneed to grow improved fodder crops to supplement existing feed resources. 'Tropical Forages':

- provides unique coverage of tropical plant-soil-animal systems in one volume

- explores key areas of current research such as resource management and thedevelopment ofsustainable systems

- outlines the fundamental principles of agricultural management, illustrated with case studies

- includes a comprehensive list of over 800 references.

'Tropical Forages' is an essential reference for agronomists, tropical agriculturalists,development agencies and resource managers involved in both arable and animal farming, andfor agricultural consultants and students of agriculture or crop science.

12

Adejuwon, J.O. and Adesina, F.A. (1990): Organic matter and nutrient status of soils undercultivated fallows: An example of Gliricidia sepium fallows from south western Nigeria.Agroforestry Systems 10:23-32.

Keywords: improved fallow; Gliricidia sepium; Nigeria; soil chemical properties; Africa.

Abstract. This paper examines the dynamics of organic matter and nutrients under plantedfallows of Gliricidia sepium in south western Nigeria, as an investigation into the behaviourof soils under such fallows. Data on soil characteristics were collected from thirty fallowfields ranging in age from one to eight years. The data sets were described using thedescriptive statistics. Furthermore, the relationships between the soil properties and the age ofthe fallow were evaluated with simple bivariate correlation analysis. Compared with publisheddata and trends in natural fallow, the study shows that the progress of the planted fallow leadsto greater organic matter build-up and increase in nitrate-nitrogen and potassiumconcentration in the soil. It also shows that the biomass retains greater amount of nutrientsduring the fallow.

13

Nnadi, L.A. and Haque, I. (1986): Forage legume-cereal systems: improvement of soilfertility and agricultural production with special reference to sub-Saharan Africa. In: Haque,I., Jutzi, S. and Neate, P.J.H. (eds.), Potentials of forage legumes in farming systems of sub-Saharan Africa. Proceedings of a workshop held at ILCA, Addis Ababa, Ethiopia, 16-19September 1985. Addis Ababa, Ethiopia: ILCA (International Livestock Centre for Africa), p.330-362.

References 39

Keywords: intercropping; cereals; nitrogen fixation; plant competition; West Africa; yields;annual field crops; maize; sorghum; legumes; undersowing.

Abstract. Intercropping forage legumes with cereals offers a potential for increasing forageand, consequently, livestock production in sub-Saharan Africa. But in such a system the yielddepression of the cereal grain should be minimal, possibly not more than 15%, for it to beacceptable to the farmer. The time of sowing of cereal and legume is critical for the yield ofeach crop. Data so far available indicate that undersowing within 10 days of planting a fastgrowing cereal such as maize does not depress cereal grain yield significantly, but with slow-growing, long-season crops such as photosensitive sorghum, grain yield is greatly depressed.In the case of sorghum, high grain yield is obtained if the legume is sown 3-4 weeks after thecereal. Intercropping forage legumes and cereals generally results in higher fodder proteinyield than cereal alone. However, fairly high yields of legumes are needed to augment thecereal residues in order to produce a feed composition capable of meeting the basal nutritionalrequirements of ruminants. The effect of intercropping on soil fertility varies withmanagement practice. It is estimated that legume roots contribute between 5 and 15 kg N/ha tosoil N under intercropping.

14

Onim, J.F.M., Mathuva, M., Otieno, K. and Fitzhugh, H.A. (1990): Soil fertility changesand response of maize and beans to green manures of Leucaena, Sesbania and pigeonpea.Agroforestry Systems 12:197-215.

Keywords: Leucaena leucocephala; Cajanus cajan; green manure; Sesbania sesban;agroforestry; maize; beans; yields.

Abstract. Three multipurpose tree species (MPTS), leucaena (Leucaena leucocephala),sesbania (Sesbania sesban var. nubica) and pigeonpea (Cajanus cajan), were pruned at aheight of 60 cm above the ground every two months, and resulting plant biomass wasincorporated into the soil as green manure. For comparison, maize (Zea mays) stover was alsoincorporated into some plots, while some other plots were left fallow. Varying quantities ofplant biomass which were incorporated into the soil over a period of 12 months caused largechanges in major soil plant nutrients, and it substantially improved soil fertility. To test forimproved soil fertility, test crops of maize and beans (Phaseolus vulgaris) were grown on thetest plots after six biomass incorporations of 4806, 13603, 16659 and 7793 kg ha-1 yr-1 forpigeonpea, sesbania, leucaena and maize, respectively. Responses of the test crops indicatedthat sesbania and leucaena green manures improved maize stover, cobs and grain yields; andbean haulms and grain yields by 77.6% when compared to fallow plots. Residual effects ofgreen manures still resulted in significant (P<0.05) yield differences in the test crop in thethird testing season. Economic significance of green manures in increasing food crop yields tosmall scale farmers is discussed.

15

Paningbatan, E.P. (1987): Alley cropping in the Philippines. In: Latham, M. (ed.), Soilmanagement under humid conditions in Asia (ASIALAND). Proceedings, 1st Regional Seminaron Soil Management under Humid Conditions in Asia and the Pacific, Khon Kaen,Phitsanulok, Thailand, 13-20 October 1986. Bangkok (Thailand): IBSRAM (InternationalBoard for Soil Research and Management), p. 385-395.


Keywords: alley cropping; Philippines; shifting cultivation; Leucaena leucocephala;Gliricidia sepium; annual field crops; soil erosion; mineral nutrients; yields; agroforestry;Alnus japonica; erosion control; sustainability; South East Asia; establishment; shrubs;legumes; legume trees.

Abstract. Comparative tests of alley cropping vs. traditional shifting cultivation system haverecently been carried out successfully in the Philippines. The main plants to be tested wereLeucaena leucocephala, Gliricidia sepium, and Alnus japonicum [A. japonica], and foodcrops were normally used between the hedgerows. An account is given of the establishmentand management of the alley crops, and their beneficial effects on erosion and nutrient inputs.Alley cropping has proved attractive to farmers, providing as it does natural levelling,increased yields and an alternative source of income from the sale of dried leaves. However,the invest-ment involved is a problem. Research is needed to assess the long-termsustainability of specific alley cropping practices, to determine the effect of alley width andalternative alley managements on soil erosion, to screen acid-tolerant shrub legumes, and tomake a socio-economic evaluation.

16

Bishop, J.P. (1983): Tropical forest sheep on legume forage/fuelwood fallows. AgroforestrySystems 1:79-84.

Keywords: tropical forest; sheep; legumes; fallow; agroforestry; agropastoral systems;Ecuador; South America; Amazon region; grazing; Desmodium ovalifolium; fuelwood; trees;Inga edulis; tropics; cassava; nitrogen; phosphorus; soil erosion; erosion; leaching; insects;diseases; weeds; fertility; crop residues; soil compaction.

Abstract. In Amazonian Ecuador, studies are being realized to intensify fallow periods bygrazing African tropical forest type sheep (Red Afro-Colombian x Barbados Black Belly) onAsian tropical forest legume cover forage (Desmodium ovalifolium) under American tropicalforest fuelwood trees (Inga edulis). The specific approach represents an innovative effort toaddress the complex problems associated with the pernicious use of less fertile lands by small-scale farmers and graziers in the humid tropics. The technologies developed are closelycompatible with traditional socio-cultural patterns. For example, shifting cultivators areencouraged to plant contour strips of legume fuelwood trees in their cassava fields. With thecassava harvest, legume cover forage is planted between the fuelwood trees, to be grazed laterby tropical forest sheep. Forage and fuelwood legumes increase soil aeration, organic matter,nitrogen and available phosphorus, control soil erosion and leaching, as well as provide abreak in cropping that checks insect, disease and weed build-ups. Tropical forest sheepimprove soil fertility by deposing organic matter which stimulates legume/Rhizobiumsymbiosis and by supplying fecal microorganisms which mineralize crop residues. In addition,tropical forest sheep cause little soil compaction and erosion, produce high quality foodprotein from legume cover forage, as well as generate cash income, capital and employmentfor small-scale farmers. Tropical forest sheep on legume forage/fuelwood fallows not onlyintensify land use under shifting field cultivation, but also form the basis for rehabilitatingalready degraded lands for further food crop production.

References 41

17

Cobbina, J. (1992): Herbage yield and soil fertility restoration potential of some tropicalforage legumes. In: Mulongoy, K., Gueye, M. and Spencer, D.S.C. (eds.), Biological nitrogenfixation and sustainability of tropical agriculture. Chichester, UK: John Wiley & Sons, p.455-462.

Keywords: soil improvement; fertility; soil chemical properties; soil organic matter; legumes;nitrogen; soil properties; sustainability; fallow; mixed farming; Stylosanthes guianensis;Pueraria phaseoloides; Centrosema macrocarpum.

Abstract. Interest in planted fallows as an alternative to shifting cultivation and related bushfallow rotation practices is gradually increasing. In mixed farming systems, adoption would beaccelerated if the planted fallow crops contributed to the farmers' livestock feed requirements.This paper reports on a study in which forage legumes were compared over a 2-year period interms of their herbage dry-matter yield and nitrogen content and their contribution toimproved soil fertility. Over long- term growth periods (8-13 months) high herbage dry-matteryields (9-16 t/ha) were produced by Stylosanthes guianensis cultivars, Pueraria phaseoloidesand Centrosema macrocarpum; the herbage nitrogen content was also very high (2.2%).Generally, there were significant improvements in soil organic carbon (90-170%) and totalnitrogen (130-240%) but not in Bray I extractable phosphorus or exchangeable potassium. Thepaper recommends a management strategy which involves incorporating into the soil some ofthe herbage produced during the fallow period before reverting to cropping.

18

Ngiumbo, K.A.B. and Balasubramanian, V. (1992): Effect of fallow and residuemanagement practices on biomass production, weed suppression and soil productivity. In:Mulongoy, K., Gueye, M. and Spencer, D.S.C. (eds.), Biological nitrogen fixation andsustainability of tropical agriculture. Chichester, UK: John Wiley & Sons, p. 463-473.

Keywords: fallow; weeds; nitrogen fixation; sustainability; natural fallow; yields; Sesbaniasesban; maize; Imperata cylindrica; soil properties; fertility; Cameroon.

Abstract. This paper presents the initial results of short-season planted fallow and residuemanagement trials in progress in Cameroon. The aim of the trials is to assess the effects ofplanted vs. natural fallow and of types of fallow residue management on biomass productionand nutrient contribution, weed suppression, and grain yields of associated and subsequentcrops. The results indicate that the top growth of the fallow vegetation provided 22-67 kgN/ha to the soil/plant system. The leaves of Chromolaena odorata, the dominant fallowspecies at one site, contributed almost the same amount of nitrogen as Sesbania sesban. In thefollowing season, the maize grain yield response to the two species was similar. The dominantfallow species at the second site, Imperata cylindrica, was poor in terms of its nitrogencontribution compared to the S. sesban intercrop treatment, and this was reflected in theresponse of the succeeding maize crop. Burning I. cylindrica gave a higher maize yield thanincorporating or surface mulching. The S. sesban intercrop effectively shaded out the weedsfor the succeeding maize crop; weed density in plots previously planted to maize/groundnutwas only slightly higher than the S. sesban intercrop treatments, but far less than that innatural fallow where the treatments involved burning, incorporation or mulching. Trials are inprogress to confirm these results and to design cost-effective planted fallow establishmentmethods for the forest zone of Cameroon.


19

Teitzel, J.K., Gilbert, M.A. and Cowan, R.T. (1991): Sustaining productive pastures in thetropics. 6. Nitrogen fertilized grass pastures. Tropical Grasslands 25:111-118.

Keywords: pastures; nitrogen; grasses; fertilization; Australia; sustainability; soil acidity;animal production.

Abstract. Nitrogen fertilized pastures are being used more in high rainfall areas as part of bothbeef and dairy production systems. Because of their productivity at critical times of the year,they have useful roles in reducing stress on other pasture types and boosting production fromgroups of cattle to match specific market requirements. On properties where cool-dry seasonmanagement is critical, higher and less seasonal production can be attained by applying Nfertilizer to a seasonally responsive grass on the deeper soils. On predominantly poorlydrained properties N application to grasses resistant to trampling on high country, allows stockreduction on low areas during the wet season. The application of 200-300 kg/ha N annuallygave near optimum milk and beef production per hectare in areas with annual rainfall greaterthan 800-1000 mm. Disadvantages of N fertilized pastures are high capital outlays in fertilizerand stock. However, under present economic conditions N fertilizer has a role in increasingproductivity and sustainability of tropical and sub-tropical property management systems. Useon special purpose pastures can lead to substantial gains in farm profitability.

20

Myers, R.J.K. and Robbins, G.B. (1991): Sustaining productive pastures in the tropics. 5.Maintaining productive sown grass pastures. Tropical Grasslands 25:104-110.

Keywords: pastures; grasses; Australia; sustainability; soil chemical properties; animalproduction; tropics; subtropics; nitrogen; sown pastures; mineralization; legumes;earthworms; trees.

Abstract. Sown grass pastures in the tropics and subtropics are initially productive, butproductivity declines with age, a process commonly referred to as run-down. Run-down isoften associated with loss of desirable species. Nitrogen (N) deficiency is the major causalfactor. The initially high production of sown pastures is a transient consequence of increasedavailable N and water that accumulates during fallow, and the run-down condition is thenormal equilibrium. The severe N deficiency in soils with apparently adequate total N is dueto progressive immobilization of N and limited mineralization of humic material. To increasethe productivity of run-down pastures, external N must be supplied or mineralization of Nfrom either soil organic matter or plant residues must be enhanced. Most potential solutionsrequire either external inputs or exploitation of finite soil reserves. Potential managementoptions under investigation that may increase productivity by increasing N supply includerotations of pastures with annual crops, sowing pasture legumes, fertilizing with N,optimizing grazing management, renovating by cultivation, establishing earthwormpopulations, establishing beneficial shade trees, and changing to stoloniferous grass types.Another more simple solution is to accept that productivity run-down will inevitably occurand to reduce stocking rate if gain per head is to be maintained.

References 43

21

Dalal, R.C., Strong, W.M., Weston, E.J. and Gaffney, J. (1991): Sustaining multipleproduction systems 2. Soil fertility decline and restoration of cropping land in sub-tropicalQueensland. Tropical Grasslands 25:173-180.

Keywords: fertility; cereals; yields; legumes; fertilizers; wheat; pastures; grasses; grass-legume pastures; farming systems; sustainability; ley farming; Australia.

Abstract. Fertile soil is the basis of sustainable agriculture. Continuous cultivation and cerealcropping lead to the depletion of soil fertility, low crop yield and poor grain quality. It isestimated that 1.2M ha of the total cropping area of 1.5M ha in southern sub-tropicalQueensland are affected by soil fertility decline, with a consequent reduction in crop yield andgrain quality valued at an output loss of $324M/yr. There is an urgent need to adopt fertilityrestorative practices to maintain economically viable farming enterprises. Legume based leys,grain legumes, fertilizer N and zero-tillage were compared for their effectiveness in restoringor maintainig soil fertility and for sustaining wheat yield and quality on a fertility-depletedbrigalow soil at Warra on the western Darling Downs. Both annual N fertilizer application andzero tillage accompanied by N application maintained wheat yields although they areuncertain options for long-term fertility restoration. The grain legume, chickpea, provided amoderate level of N supply to the following wheat crop but is also an uncertain option forfertility restoration. Pasture leys based on annual and perennial legumes, with or withoutgrasses, provide a useful option for fertility restoration. One year medic and lucerne leyscontributed to soil N to a moderate level although lucerne leys may have an adverse effect onthe moisture available for following crops. Grass-legume mixed pastures increased soilfertility as measured by an increase in soil total N. Of these options, pastures based on annualand perennial temperate legumes and tropical grasses have the potential to increase ormaintain soil fertility. Legume leys and especially grass-legume pasture leys will play a keyrole in future ecologically and economically sustainable farming systems.

22

Reddy, K.C., Soffes, A.R. and Prine, G.M. (1986): Tropical legumes for green manure. I.Nitrogen production and the effects on succeeding crop yields. Agronomy Journal 78:1-4.

Keywords: legumes; green manure; annual field crops; nitrogen uptake; yields; nitrogenfixation.

Abstract. The energy shortage of the 1970s and knowledge that N prices may continue toescalate renewed interest in growing legume green manure crops to furnish N. The objectiveof this study was to evaluate the ability of selected green manure crops to furnish N tosucceeding crops. This study evaluated seven tropical legumes and a marigold (Tagetes erectaL.) cv. "Cracker Jack" grown for different lengths of the summer under fumigation (F) andnonfumigation (NF) on Aredondo fine sand (loamy, siliceous, hyperthermic GrossarenicPaleudults) during 1979, 1980, and 1981. Spilt-plot and randomized complete block designswith five replications were used. In the basic experiment, fumigation and nonfumigation weremain plots and tropical legumes and fallow were the subplots. The green manure crops weregrown for three different periods, early summer, full summer, and late summer. Early and latesummer plantings usually included only the legume crops and fallow in a randomizedcomplete block design. Average top growth N yields in kg ha-1 were 40 for "PI 305070"mungbean (Vigna radiata (L.) Wilcz.), 250 for "Norman" pigeonpea (Cajanus cajan (L.)


Millsp.), 190 for "FL 81d" pigeonpea, 170 for showy crotalaria (Crotalaria spectabilis Roth.),220 for hairy indigo (Indigofera hirsuta L.), 170 for jointvetch (Aeschynomene americana L.),190 for velvetbean (Mucuna deeringiana (Bort.) Merr.), and 60 for marigold. The dry matteryield of legumes (harvested before seeding) with higher N yields usually exceeded 10000 kgha-1 for full-season production in all three years. Fumigation increased dry matter yield oflegumes and marigold, but not their N yield. The grass crops, rye (Secale cereale L.), ryegrass(Lolium multiflorum L.), maize (Zea mays L.), and wheat (Triticum aestivum L.) producedsignificantly higher dry matter (up to 100%) when planted after green-manure summerlegumes than when planted after summer fallow. Calculated uptake of N from green manureby these grass crops was relatively low, averaging from -2 to 23 kg ha-1. Applying 50 and 100kg N ha-1 as ammonium nitrate to the green-manured plots did not increase recovery of Nfrom green manure by wheat.

23

Palm, C.A. and Sanchez, P.A. (1991): Nitrogen release from the leaves of some tropicallegumes as affected by their lignin and polyphenolic contents. Soil Biology and Biochemistry23:83-88.

Keywords: nitrogen; legumes; lignin; polyphenolics; mineralization; live mulch; greenmanure; ground cover; mulch; chemical composition; manure; rice.

Abstract. Leguminous plant materials used as mulches, green manures and cover crops aregenerally assumed to provide a readily-available source of N to crops. However, little isknown about the chemical composition and N release patterns of the variety of legumes beingused in tropical agroecosystems. N release patterns from the leaflets of 10 tropical legumesand rice straw were determined in a laboratory experiment. Ground leaf material was allowedto decompose in an acid soil (pH 4.5) for 8 weeks and the soil was analyzed periodically forextractable NH4

+ -N and NO3− -N. N release in the soil plus plant material were compared to

that of the soil without plant material added and related to the N, lignin and polyphenolicconcentrations of the leaflets. Three patterns of net N mineralization emerged during the 8weeks. One pattern exhibited by the control soil, rice straw and leaves of two of theleguminous plants was a low, positive net mineralization. Another pattern showed muchhigher rates of mineralization than the control soil and the third pattern showed initial netimmobilization followed by low but positive net mineralization rates. The amount of Nmineralized during the 8 weeks as compared to the control soil ranged from +46 to -20% ofthe N added in plant material. Net mineralization was not correlated to % N or % lignin in theleaf material but was found to be negatively correlated to the polyphenolic concentration, r = -0.63, or the polyphenolic-to-N ratio, r = -0.75. Mineralization in excess of the control soil wasfound only for materials with a polyphenolic-to-N ratio <0.5. Mechanisms to explain the lowmineralization by materials high in polyphenolics include the formation of stable polymersbetween polyphenolics and amino groups, and nitrosation, a chemical reaction of nitrite( NO2

− ) with polyphenolics. Our results show that leguminous plant material with a highpolyphenolic content or polyphenolic-to-N ratio may not be a readily-available source of N.

References 45

24

Williams, W.A. (1967): The role of the Leguminosae in pasture and soil improvement in theNeotropics. Tropical Agriculture (Trinidad) 44:103-115.

Keywords: pastures; legumes; grassland; nitrogen; grasses; livestock; Centrosema pubescens;Pueraria phaseoloides; Stylosanthes; green manure; manure; rice; soil improvement.

Abstract. The present use of tropical legumes in the western hemisphere is evaluated, andprofitable areas for further investigation and development are outlined. Studies of soil organicmatter from sites ranging from 4° to 20° N latitude show that many tropical soils developedunder forest are well supplied with humus, and the use of Leguminosae for their nitrogen-fixing ability is not justified until the nitrogen-supplying power of the soil declinessubstantially. For pasture and crop production on grassland soils, well-adapted legumesshould be considered along with alternate sources of nitrogen since grassland soils have a verylimited nitrogen-supplying power. The use of legumes for pasture and forage crops meritsspecial attention wherever there is an annual dry season that stops growth of forage grasses,thus reducing their protein below livestock requirements. Several promising legumes arebeing studied, and some are being planted commercially on a limited scale, e.g. Centrosemapubescens, Glycine javanica, Leucaena glauca, Lotononis bainesii, Phaseolus atropurpureus,Pueraria phaseoloides, and Stylosanthes gracilis. A useful role for legumes purely for soilimprovement requires more extensive, positive evidence. An exception is the use ofleguminous green manure in the production of paddy rice, where the reduced condition of theflooded soil provides a special advantage in highly efficient nitogen use. Soil improvement bylegumes is also a worthwhile adjunct to their use primarily for pasture production or for shadein shade-grown crops. The symbiontic nitrogen-fixing ability of tropical legumes has receivedlittle attention in neotropical microbiology thus far. Investigations in this area will berewarding for both practical and theoretical aspects of rhizobial biology.

25

IRRI (ed.) (1988): Green Manure in Rice Farming. Proceedings of a symposium onsustainable agriculture, IRRI, 25-29 May 1987. Los Baños (Philippines): IRRI (InternationalRice Research Institute), 379 p.

Keywords: rice; West Africa; legumes; Asia; soil chemical properties; green manure; farmingsystems; sustainability.

Abstract. This book contains the proceedings of a symposium on the role of green manurecrops in rice farming systems held in 1987. General knowledge and technologies fromdifferent regions of Asia and West Africa are reported and the ability of several plant speciesto tolerate the soil and water conditions of flooded rice fields are discussed. Furthermore, theeffects of green manure crops on soil fertility are analized, with emphasis on biological N2-fixation, transformation of green manure nitrogen and changes in the physicochemicalproperties of irrigated rice soils. Detailed information is given about integrated use of legumesin rice farming systems and on the fields of seed production and collection of tropical legumegermplasm.


26

Gibson, T. (1987): A ley farming system using dairy cattle in the infertile uplands. WorldAnimal Review 61:36-43.

Keywords: ley farming; farming systems; cattle; tropical highlands; Thailand; crop rotation;pastures; yields; annual field crops; dairy cows; animal production.

Abstract. The rotation of sown pastures with crops (ley farming) increases crop yields.However, a substantial return from the pasture (ley) phase must be obtained if farmers indeveloping countries are to gain economically from this system. The author describesexperiments in the infertile uplands of northeast Thailand, the poorest region of the country,where it has been shown that dairy cattle can be raised with a small cash input, and that themilk produced can be sold to generate income. To overcome sociological constraints, it issuggested that the ecologically sound ley farming system be introduced through milkproduction, the aim being eventually to extend the system to beef cattle and buffaloproduction, which are more widespread.

27

Haynes, R.J. (1983): Soil acidification induced by leguminous crops. Grass and ForageScience 38:1-11.

Keywords: soil acidity; legumes.

Abstract. Solution culture and greenhouse studies have both clearly demonstrated the abilityof legumes to acidify their rooting medium. Furthermore, research workers comparing the pHbeneath undisturbed sites versus all-legume pastures or all-grass versus all-legume (or grass-legume) pastures have observed a lower soil pH under the leguminous pastures. The processesleading to legume-induced soil acidification are reviewed and discussed. The growth oflegumes which are fixing atmospheric N2 involves the excess uptake of nutrient cations overanions from soil solution. This results in the net efflux of H3O

+ ions from plant roots into therhizosphere. When virgin lands are sown with legumes the accumulation of soil organicmatter, with a consequent increase in cation exchange capacity and exchange acidity, is animportant contributing factor to the long-term decline in surface soil (0-10 cm) pH.Nonetheless, such a phenomenon does not explain the decrease in pH below 10 cm soil depthnor the lower pH below leguminous than all-grass pastures. The efflux of H3O

+ ions from thelegume roots may have an important effect on the soil pH under such conditions. The loss ofsymbiotically fixed N2 from the system through leaching of NO3

− -N may also contribute tosoil acidification under leguminous pastures.

28

Godefroy, J. and Bourdeaut, J. (1972): Action des plantes de couverture sur les carac-téristiques chimiques, biologiques et structurales d'un sol de verger de Côte d'Ivoire. Fruits27:349-353.

Keywords: Stylosanthes gracilis; cover crops; soil chemical properties; soil physicalproperties; Pueraria javanica; plant competition; fruit orchards.

Abstract. The agro-pedological conditions of a soil under citrus plantation in relation to threedifferent treatments were investigated. The treatments were natural vegetation cover,

References 47

Stylosanthes gracilis cover and Pueraria javanica cover. Chemical soil properties as well asmicrobial activity were more favourable under natural vegetation or Stylosanthes cover thanunder Pueraria cover. From the point of view of soil structure, both cover crops were superiorto natural vegetation. Utilisation of Stylosanthes as a cover plant in fruit orchards seems to beinteresting as it requires less labour than management of natural vegetation or Pueraria cover.(Abstract by bibliography authors)

29

Moore, A.W. (1962): The influence of a legume on soil fertility under a grazed tropicalpasture. Empire Journal of Experimental Agriculture 30:239-248.

Keywords: legumes; fertility; pastures; grasses; grass-legume pastures; Nigeria; Centrosemapubescens; nitrogen; nitrogen fixation; phosphorus.

Abstract. Soil fertility under two-year-old grazed pure grass and mixed grass-legume pastureswas studied at University College, Ibadan, Nigeria. The inclusion of 'centro' (Centrosemapubescens) in a giant stargrass (Cynodon plectostachyus) pasture resulted in significantlyhigher levels of organic matter, total nitrogen and nitrifiable nitrogen in the underlying soil.The total nitrogen content under the pasture containing the legume was 250 lb. nitrogen peracre-ft. per annum higher than that under the pure grass stand. This is attributed to symbioticnitrogen fixation by the centro and is of the same order of magnitude as values reported fornitrogen fixation by temperate legumes. There were no differences in carbon: nitrogen ratiosunder the two pastures; this emphasizes the importance of a legume in tropical pastures andleys if they are to build up soil organic matter satisfactorily. No significant differences inavailable phosphorus, pH, or percentage of material finer than coarse sand, resulted from theinclusion of centro. The inclusion of centro raised the nitrogen content of the associated giantstargrass from 1.8 to 2.4 per cent. There were, however, no significant differences inphosphorus, calcium, magnesium, or potassium contents of the stargrass as a result of itsassociation with centro.

30

De, R., Yogeswara Rao, Y. and Ali, W. (1983): Grain and fodder legumes as precedingcrops affecting the yield and N economy of rice. Journal of Agricultural Science 101:463-466.

Keywords: legumes; fertilization; nitrogen uptake; rice.

Abstract. Experiments made for 2 years on a sandy-loam soil showed that previous graincrops of mung bean (Vigna radiata), cow pea (V. unguiculata) and black gram (V. mungo)increased the grain and straw yield of a subsequent crop of rice relative to previous foddercrops of maize or guar bean (Cyamopsis tetragonoloba) or a grain crop of Phaseolus bean(Phaseolus vulgaris). The benefits from preceding crops of mung bean, cow pea or blackgram were equivalent to 36-67 kg N/ha of chemical fertilizer applied to the rice cropfollowing a cereal. The legumes improved yield-contributing characters such as number ofproductive tillers/m2, panicle length and number of grains/panicle. The yield increase from thepreceding legumes was noted even when the rice crop was given increasing rates of fertilizerup to 90 kg N/ha.


31

Adil, M.L., Kathavate, Y.V. and Sen, A. (1966): Changes in soil associated with continuousgrowth of some vegetation. Plant and Soil 15:73-80.

Keywords: grasses; legumes; Tephrosia candida; Medicago sativa; nitrogen; soil pH; soilchemical properties; soil organic matter; soil physical properties; Imperata cylindrica;Pennisetum orientale; Pennisetum polystachyum; Pueraria hirsuta.

Abstract. From a study of the composition of the soil and the subsoil under three grasses,Imperata cylindrica, Pennisetum orientale, Pennisetum polystachyum and three legumesTephrosia candida, Medicago sativa and Pueraria hirsuta and those of natural bare soil in theneighbourhood of each, it could be observed that the soils under vegetation contained moremoisture, organic matter, organic nitrogen clay and soluble salts but had lower pH values thanthe bare soils. The soils under grasses had less moisture, lower pH and lower salinity buthigher clay content and exhibited greater aggregation than the soils under legumes. Thoughthe soils under grasses had significantly higher quantities of organic matter than the soilsunder legumes there was no significant difference in the organic nitrogen contents betweenthem.

32

Yost, R.S., Evans, D.O. and Saidy, N.A. (1985): Tropical legumes for N production: growthand N content in relation to soil pH. Tropical Agriculture (Trinidad) 62:20-24.

Keywords: legumes; nitrogen fixation; soil acidity; yields; green manure; erosion control; livemulch; soil chemical properties; manure; maize; erosion.

Abstract. Growth rates, N accumulation, and soil cover potential of six green manure legumeswere compared on a manganiferous Oxisol. Responsiveness of Crotalaria juncea L., Mucunasp., Lablab purpureus (L.) Sweet, Psophocarpus tetragonolobus (L.) DC, Sesbaniagrandiflora (L.) Pers. and Sesbania cannabina Poir. to increasing soil pH (4.7-6.9) wasexamined in a field experiment. N content of the legumes was compared with that of Zeamays L. to estimate N2 fixation by the legumes. Dry matter and N content increased withincreasing pH to > 6.0. When N yield at pH 4.7 was expressed as a percentage of maximum Nyield, S. cannabina was most sensitive to low pH (3%), followed by lablab (16%), crotalaria(20%), mucuna (36%), and maize (70%). N accumulation in the tops of S. grandiflora andCrotalaria ranged from 10 to 72 kg N/ ha, respectively, during the 10-week growth at soil pHof 5.8. Maize growth and N percentage indicated low levels of available soil N, suggestingthat legume N content resulted primarily from the plant-rhizobia symbiosis rather than from Nrecovery from soil. High levels of soil Mn were probably the principal limitation to legumegrowth at pH < 5.3. Mucuna and lablab provided the greatest and most rapid initial soil coverand thus should be most effective in controlling soil erosion by rainfall.

33

Jayasinghe, C.K. (1991): The role of leguminous cover crops in soil improvement withspecial reference to the nitrogen economy of tropical rubber soils. Bulletin of the RubberResearch Institute of Sri Lanka 28:23-26.

References 49

Keywords: nitrogen; Pueraria phaseoloides; Desmodium ovalifolium; Centrosema pubescens;erosion; legumes; trees; nitrogen fixation; cover crops; Sri Lanka; Mimosa invisa;Calopogonium mucunoides; Hevea brasiliensis; live mulch; soil organisms; soil physicalproperties; soil chemical properties.

Abstract. The use of leguminous cover crops is standard practice in rubber plantations of SriLanka, in order to improve the biological, chemical and physical properties of the soil. Fivecover crops are commonly used: Pueraria phaseoloides, Desmodium ovalifolium, Mimosainvisa, Calopogonium mucunoides, and Centrosema pubescens. Cover crops reduce soilerosion in sloping lands, shade the soil from direct sunlight, and add organic matter.Leguminous cover crops enhance the biological activity of the soil and fix most nitrogen.When rubber plants were grown in sown legume plots, the growth of the trees, and the dryweight and N content of the leaves were higher than those of rubber trees grown in plots withnatural cover. Decomposition products of the cover crops improved the nitrogen economy ofthe soils. Leguminous cover crops grown with rubber trees imparted a beneficial effect onplantation soils.

34

Cadisch, G., Sylvester-Bradley, R. and Noesberger, J. (1989): 15N-based estimation ofnitrogen fixation by eight tropical forage-legumes at two levels of P:K supply. Field CropsResearch 22:181-194.

Keywords: nitrogen; Centrosema acutifolium; nitrogen fixation; Centrosema macrocarpum;Zornia glabra; Pueraria phaseoloides; Desmodium ovalifolium; Stylosanthes macrocephala;Stylosanthes guianensis; Stylosanthes capitata; fertilizers; phosphorus; legumes; Colombia;micronutrients; grasses; Oxisols; yields.

Abstract. Ca, S, Mg, Zn, Cu, B and Mo, with or without 80 kg P + 70 kg K/ha were applied toCentrosema acutifolium, C. macrocarpum, Zornia glabra, Pueraria phaseoloides,Desmodium ovalifolium, Stylosanthes macrocephala, S. guianensis and S. capitata at the startof the rainy season one year after establishment and effects on growth and nitrogen fixationwere evaluated under a cutting regime by using the 15N dilution technique. Rooting patternand nodulation were also evaluated. The relative N accumulation curves of the legumes andcontrol (savanna grasses) were studied in a separate experiment. The legumes wereestablished in furrows separated by native savanna in an Oxisol of the Eastern Plains ofColombia to give a density of 5-6 plants/m². With PK fertilizer, all legumes derived at least70% of their N from the symbiosis (% Ndfa), whereas without PK both lower values and largerdifferences in the % Ndfa (44-84% Ndfa) between species were observed. The greatest effect ofPK on % Ndfa was observed in D. ovalifolium (70 and 44% Ndfa with and without PK,respectively), but the effect on its yield was relatively small. S. macrocephala responded witha large increase in yield (380% with PK), although it was the only species in which PK did nothave a significant effect on % Ndfa. Total shoot N derived from fixation with PK fertilizerranged from 25 kg/ha for D. ovalifolium to 115 kg for P. phaseoloides, with three periods ofgrowth over a total of 17 weeks. Without PK fertilizer, 11-48 kg N/ha were derived fromfixation. Legume ranking for total N derived from fixation mostly reflected yield differences.However, D. ovalifolium ranked lower for total N from fixation than for yield due to its low %Ndfa and low N concentration.


35

Thomas, R.J. (1992): The role of the legume in the nitrogen cycle of productive andsustainable pastures. Grass and Forage Science 47:133-142.

Keywords: legumes; nitrogen; nitrogen cycle; pastures; fertilizers; nitrogen fixation; yields.

Abstract. The N cycle in grazed temperate and tropical pastures receiving no N fertilizer wasstudied by simulating N fluxes in different parts of the cycle. Estimates of N required to befixed by legumes to balance the cycle without reducing soil organic N reserves ranged from 38to 53% of aboveground herbage N (20-31% on a DM basis) for tropical pastures with pastureutilization levels of 10-40%. In intensively grazed temperate pastures with utilization levels of50-70%, the N input required from legumes was 57-67% of the aboveground herbage N (35-45% on a DM basis). Variations in the amounts of internally cycled N would have the greatestimpact on the requirement for N2 fixation in poorly utilized pastures, whereas variations in therecovery of N in excreta would have the greatest effect in intensively grazed pastures. Theamounts of biologically fixed N required to give sustainable herbage DM yields of 3-22 tDM/ha per year were calculated as 15-158 kg N/ha annually in tropical pastures. Forintensively managed temperate pastures producing 6-15 t DM/ha per year with an N content of3.5%, 120-352 kg fixed N/ha per year was required. It was suggested that legume contents of20-45% of herbage DM could provide sufficient N for sustainable productive pastures.

36

Lal, R., Wilson, G.F. and Okigbo, F. (1979): Changes in properties of an Alfisol producedby various crop covers. Soil Science Society of America Journal 127:377-382.

Keywords: grasses; soil properties; Stylosanthes; soil organic matter; nitrogen; infiltration;fallow; soil bulk density; cation exchange capacity; Brachiaria; Paspalum; Cynodon;Pueraria; Centrosema.

Abstract. The effects of three grasses and five leguminous covers, grown on an erodedtropical Alfisol for two years, on soil properties were investigated. Improvements in soilcharacteristics under Brachiaria, Paspalum, Cynodon spp., Pueraria, Stylosanthes,Stizolobium, Psophocarpus, and Centrosema were compared with that of weed-fallow control.There were significant improvements in soil organic matter, total nitrogen, cation exchangecapacity (CEC), infiltration rate, moisture retention at low suctions, and soil bulk densityunder various grass and leguminous fallow compared with control.

37

Yamoah, C.F. and Mayfield, M. (1990): Herbaceous legumes as nutrient sources and covercrops in the Rwandan highlands. Biological Agriculture and Horticulture 7:1-15.

Keywords: legumes; maize; live mulch; erosion control; tropical highlands; Rwanda.

Abstract. Herbaceous legumes were assessed for their suitability as nutrient sources and asground cover for the northern highlands of Rwanda. There were three investigations whichfollowed the Farming Systems Research (FSR) methodology. First, exploratory studies wereconducted to measure biomass yield and percentage ground cover. Second, 12 legumes werescreened on station for biomass production, nutrient yield and ground cover. Yields of maize(Zea mays) grown as a test crop following incorporation of the legumes were compared with

References 51

yields of maize grown at different nitrogen levels. Third, following farmers' comments on thesecond study's results, five legume species were chosen for multilocational testing on 11farmers' fields. Preliminary studies showed high biomass yields and good ground cover forDesmodium sp., Trifolium sp. (red clover), Vetch and Stylosanthes sp., Trifolium repens(white clover) demonstrated a prostrate and complete ground cover - ideal characteristics forlive mulch species. On-station experiments indicated significant accumulation of nutrients bythe legumes, but with substantial site-species interaction. Legumes with high biomass yieldsdecreased maize yields when compared with maize grown with no nitrogen. Themultilocational testing confirmed the inconsistent performance of the species at different sitesand led to the definition of three sub-regions (North, Central and South) for which differentpromising legumes were selected. Selection criteria such as vegetative yield, nutrient contentand ground coverage resulted in the following selections by region and in order of preference:North: Canavalia, Lupin, Mucuna; Central: Vetch, Lupin; and South: Mucuna, Lupin and (onfertile soil) Canavalia. In terms of legume growth performance, this study suggests possiblebenefits from 1) moderate initial fertilization, 2) extended vegetative growth, 3) high sowingdensities and 4) sowing in mixtures on infertile soils. Short-term crop yield losses due to netimmobilization of soil nutrients by some cover crops (e.g. Vetch) may make legumesunacceptable to small-scale farmers. Research on decomposition and nutrient release isrecommended prior to extension of legumes to farmers.

38

Brasil, E.C., Burger, D., Flohrschuetz, G.H.H., Lenthe, H.R., Stolberg-Wernigerode,A.Graf zu and Wollersen, T. (1991): Utilization of "Capoeira" as a source of organicfertilizer. In: Studies on the utilization and conservation of soil in the eastern Amazon region,Eschborn (Germany): Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), p. 199-216.

Keywords: Amazon region; mulch; improved fallow; legumes.

Abstract. The possibility of using "Capoeira" as a source of organic fertilizer without fire wasstudied in two experiments. In the first, on parcels where the "Capoeira" was felled but notburnt, it was verified that the soil's carbon content increased, and the chemical fertilizerapplied (principally P and K) had more a positive effect than on the parcels where the"Capoeira" had been burnt. On the fertilized and unburnt parcels, the corn production wasgreater as of the second year than that of the fertilized and burnt parcels. This tendency wasless pronounced with the cowpea production, where the unburnt and unfertilized parcelsproduced significantly more than the burnt and fertilized parcels only as of the fourth year.The system tested in the first experiment is not viable, because of the excessive amount oflabour necessary for the preparation of the area and for its cultivation during the first fewyears, and also because of the unfavourable production of the first year. In the secondexperiment, various techniques and equipment for the preparation of "Capoeira" areas withoutfire were explored. The feasibility of felling "Capoeira" and not burning it was confirmed.Leguminous species were sown in order to cover the felled matter, facilitating thedecomposition, and to increase the N-content of the biomass. This vegetation was cut downmechanically at the end of the year. A more detailed study of this technique was initiated ontwo farming areas. Various leguminous species were compared, as was the use of biomass cutup as mulch and mixed with the soil.


39

Burger, D. and Brasil, E.C. (1991): Production of organic fertilizers in the alley-croppingsystem. In: Studies on the utilization and conservation of soil in the eastern Amazon region,Eschborn (Germany): Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ), p. 217-236.

Keywords: alley cropping; Amazon region; mulch; legumes; sustainability.

Abstract. The alley-cropping system aims to maintain the soil's fertility level through theapplication of organic fertilizer produced on the same location. Alternating rows of cash cropsand strips of organic matter producers were planted. The latter were periodically cut to beapplied as mulch to the cash crops. The experiment was set up in 1985 and 1986 on threelocations in the municipality of Capitão Poço, PA, and on five locations in the municipality ofIgarapé-Açu, PA. On three locations in the municipality of Igarapé-Açu, the legumes receivedan initial fertilization of 10 kg N/ha and 60 kg P2O5/ha. A total of 13 producer species oforganic matter were tested, and with some, a large production of biomass was obtained withina mere 24 weeks: Cassia rotundifolia 9.2 t/ha, Cajanus cajan 7.9 t/ha, and Crotalaria paulina7.7 t/ha in areas with chemical fertilizer, and Cajanus cajan 6.7 t/ha and Crotalaria paulina6.1 t/ha in areas without chemical fertilizer. The quantity of phosphorus contained in theorganic fertilizer produced was insufficient to meet the crop needs. On the other hand, largequantities of nitrogen and potassium were obtained with the organic matter harvested. In theunfertilized area, 222 kg N/ha and 159 kg K2O/ha were obtained with Cajanus cajan in 58weeks. The organic fertilizer produced with Cajanus cajan per hectare without chemicalfertilizer in 24 weeks contained as much nitrogen as is removed with a 20 t/ha cassavaharvest. The organic fertilizer produced in 40 weeks contained the equivalent of this harvest inK2O. The organic fertilizer produced with this species in half a year contained the equivalentin nitrogen and K2O of a 2.22 t/ha corn harvest. Thus the system demonstrated an excellentpotential for maintaining the soil's fertility. The management of this system should be studiedin greater detail, especially the cutting intervals, the distance between plant producers oforganic matter and cash crops, the forms of application of organic matter, and the economicsand ergonomics of the system.

40

Lascano, C.E. (1991): Managing the grazing resource for animal production in savannas oftropical America. Tropical Grasslands 25:66-72.

Keywords: animal production; pastures; cattle; tropical savanna; sustainability; Colombia;South America; grasses; grass-legume pastures; soil acidity.

Abstract. Research carried out to evaluate management options and animal productionpotential of native and improved pastures in savanna regions of tropical America is reviewed,with emphasis on Colombia's Eastern Plains. In areas with limited infrastructure, nativegrasses are the main forage resource and weight gains of cattle grazing these native pastureswith burning and mineral supplementation vary from 70 to 90 kg/ha and from 15 to 20 kg/ha.As infrastructure improves, the strategic use of grass-legume pastures to complement thenative savanna, together with the use of mineral supplementation, could increase individualweight gains by 40 percent. In savanna areas with good infrastructure, improved grassesadapted to acid soils replace the native vegetation and, together with mineral supplementationand appropriate grazing management, increase animal production/unit area 10 times compared

References 53

to native pastures. However, these pastures do not persist over time because of N deficiencyand pests. The highest and more stable gains could be obtained with legume-based pastures,which, in turn, depend on high management inputs. On the acid soils of tropical Americansavannas, these legume-based pastures can play an important role in agropastoral systems.

41

Myers, R.J.K. (1976): Nitrogen accretion and other soil changes in Tindall clay loam underTownsville stylo/grass pastures. Australian Journal of Experimental Agriculture and AnimalHusbandry 16:94-98.

Keywords: nitrogen accretion; pastures; Stylosanthes humilis; phosphorus; legumes;fertilizers; establishment; soil properties; Australia.

Abstract. Soil changes after 3-15 years of fertilized leguminous pastures on Tindall clay loamsoil at Katherine, N.T. were studied by comparison of leguminous pasture soils with theirnative counterparts. Soil organic carbon, total nitrogen, C/N ratio and pH were unchanged bythe presence of Townsville stylo (Stylosanthes humilis). Available phosphorus (bicarbonateextraction) was significantly higher under legume pasture, reflecting its fertilizer history, butthere was no pattern of increase with time, nor with quantity of fertilizer. Available nitrogen(boiling water extraction) was higher under legume pasture, and both the absolute value underlegume pasture and the change in amount were correlated significantly with the age of thepasture. Available nitrogen after three years of legume pasture was equal to that underunimproved pasture, suggesting that gains in this period merely balanced losses duringclearing and establishment.

42

Tarawali, G. (1991): The residual effect of Stylosanthes fodder banks on maize yield atseveral locations in Nigeria. Tropical Grasslands 25:26-31.

Keywords: Stylosanthes; maize; yields; Nigeria; natural pastures; natural fallow; fodder banks;annual field crops; Africa.

Abstract. The response of maize to N on natural pasture (fallow), or following Stylosanthespastures (fodder banks) was investigated at 4 locations in central Nigeria. Maize planted in thefodder banks outyielded that on the natural fallow at each level of applied N. Without appliedN, the average grain yields were 1.7 t/ha in the fodder bank and 0.8 t/ha in the natural pastureareas. In well managed fodder banks, the maximum yield of maize was obtained at 60 kg/ha Nin comparison with the recommended rate of 120 kg/ha N for a natural fallow or continuouslycultivated soil. In the first year of cropping 45 kg/ha N had to be applied to maize grownoutside the fodder banks to produce the same grain yield as unfertilized maize following agood Stylosanthes pasture. Grain yields of maize were lower in the second year but again,higher yields were obtained from inside than outside the fodder bank areas. The response ofmaize inside the Stylosanthes pastures was discussed in relation to land history and the way inwhich the pastures were managed.


43

Lloyd, D.L., Smith, K.P., Clarkson, N.M., Weston, E.J. and Johnson, B. (1991):Sustaining multiple production systems. 3. Ley pastures in the subtropics. TropicalGrasslands 25:181-188.

Keywords: pastures; subtropics; Australia; ley farming; sustainability; agropastoral systems;legumes; yields; annual field crops; grasses.

Abstract. During the 1990s, wheat protein and yield from many cropping soils (mainlyvertisols) in the subtropical wheat belt will continue to decline as soil fertility is graduallydepleted. One option for maintaining crop yield and quality is ley farming. It has had limitedapplication when soil fertility has been adequate for crops and where the use of N fertilizerhas been a viable option. Temperate legumes of the genus Medicago (lucerne and annualmedics), and tropical grasses are available for use in leys, but there are currently no suitabletropical legumes. The increases in yield and quality of grain crops recorded after lucerne andannual medic leys in various experiments are reviewed and related to changes in soil N andother factors. Leys provide more enduring benefits to subsequent crops than does theapplication of fertilizer N. Ley farming is productive, suitable, and provides a greater hedgeagainst climatic and economic risks than cropping alone. However, it requires a wider rangeof management skills, and the challenge remains to stimulate wider adoption of this system.

44

Fox, R.L., Hue, N.V., Jones, R.C. and Yost, R.S. (1991): Plant-soil interactions associatedwith acid, weathered soils. Developments in Plant and Soil Science 45:197-204.

Keywords: soil acidity; legumes; yields; soil chemical properties; leaching.

Abstract. Plant-soil interactions in weathered soils are so complex that unqualified statementsabout a suitable pH for plants are risky. Conventional experimental designs and statisticalmethods may not be appropriate for investigating such complexities. Lime experiments usingcontinuous function designs and observation of plant response to indigenous variability in soilpH permit detailed observations of plant-soil interactions that are frequently not detected. Agraphical boundary-line approach to interpreting data can make good sense out of apparentconfusion. Increasing the pH of variable-charge soils by adding lime or by indigenous meansincreased CEC and retarded cation leaching, but Ca solubility changed very little over therange pH 5 to 6. N2 fixation and yield was closely related to soil pH, soil Mn and Mn uptakeby soybean. This result was clearly demonstrated regardless of numerous other limitingfactors. Plant yield response curves resolved into distinct segments that corresponded withassociated soil properties. Excess Al compounded by Ca deficiency is suspect in the pH range< 5. Excess Mn, and Ca deficiency probably limited yields in the pH range 5.0 to 5.7. Yieldswere stable, and Ca and P were constant in the pH interval 5.7 to 6.0. Yields abruptlyincreased in the pH interval 6.0 to 6.3. This was associated with elevated Ca concentrations insoil solutions.

45

Chamberlin, R.J., Peake, D.C.I., McCown, R.L., Vallis, I. and Jones, R.K. (1986):Competition for nitrogen between a maize crop and forage legume intercrops in a wet-drytropical environment. In: Haque, I., Jutzi, S. and Neate, P.J.H. (eds.), Potentials of forage

References 55

legumes in farming systems of sub-Saharan Africa. Proceedings of a workshop held at ILCA,Addis Ababa, Ethiopia, 16-19 September 1985. Addis Ababa (Ethiopia): ILCA (InternationalLivestock Centre for Africa), p. 82-99.

Keywords: nitrogen; maize; forage legumes; legumes; intercropping; Alysicarpus vaginalis;Stylosanthes hamata; Centrosema pascuorum; plant competition; nitrogen uptake; yields;seed production; seeds.

Abstract. Growth and yield of maize as a sole crop was compared with that of maize withintercrops of Alysicarpus vaginalis, Stylosanthes hamata cv. verano, or Centrosemapascuorum under conditions in which soil water was adequate prior to physiological maturityof the crop. Data from three seasons are presented. In the first season, when only one N ratewas used with a range of legume densities, maize yield varied inversely with legume yield. Inthe other two seasons N rate was varied, and 15N was used to obtain more information on thecompetitive relationships between the components of the intercropping systems. Results showthat when conditions are good for establishment and early growth of the legumes, competitionbetween the legume intercrop and maize occurs. This effect was greatest at low N rates andless with verano stylo than with A. vaginalis. There was never any evidence of a positivecontribution by any of the legumes to the N economy of maize. Legume seed production,essential for regeneration of the legume in the cropping system being studied, varied withspecies and seasonal conditions.

46

Boonman, J.G. (1993): From shifting cultivation to crop-grass rotations. In: Boonman, J.G.(ed.), East Africa's grasses and fodders: ecology and husbandry. Dordrecht/NL: KluwerAcademic Publishers, p. 65-85.

Keywords: shifting cultivation; grasses; Africa; cattle; fallow; weeds; yields; soil erosion;erosion; fertility; manure; livestock; mixed farming; pastures.

Abstract. Farmers in East Africa want cattle, but they need crops. In conventional subsistenceagriculture a fallow period of long duration used to be employed to restore the productivecapacity of the soil. As pressure on land increased, systems of husbandry processed fromshifting cultivation to grass weed fallows which were grazed but on better soils to continuouscropping. Except on the most stable and fertile soils, continuous cropping rapidly leads todiminishing yields, nutrient depletition and soil erosion. The need to maintain fertility appliesto all soils. In the 1930s attention turned to the positive role grass fallows were observed toplay in conventional shifting cultivation. It was subsequently realized that cultivated grassesare able to restore fertility in a shorter time and more effectively then when land is abandonedto volunteer grasses which, by their very nature, are crop weeds (e.g. African Couchgrass).Cultivated grasses help to suppress these weeds. Grasses add effective fresh OM and N, andcan draw up minerals from lower soil depth through a deep and extensive root system. Amajor effect is that of improving soil structure and consequent water economy throughaggregate stability, permeability and root channels. The latter aspects distinguish grasses fromorganic manures. More rain water is trapped on the soil surface and subsequently held in thesoil profile; the risk of erosion is reduced. Grasses can double the yield of following crops,while grazing is more beneficial to such crops than when grass is mown and removed.Measurable improvements in topsoil structure may vanish early but yield responses remainsignificant for a long period. Crops and livestock, via better grasses, benefit directly by crop-grass rotations, but the long-term beneficiary is the soil. Alternate husbandry is typical of


farming in East Africa, whether subsistance or commercial. Mixed-farming, based onalternating grazed pastures with crops, is still a solid platform from which efforts for sustaineddevelopment can be launched, in the nearest possible harmony with the environment.

47

Vallis, I. (1983): Uptake by grass and transfer to soil of nitrogen from 15N-labelled legumematerials applied to a Rhodes grass pasture. Australian Journal of Agricultural Research34:367-376.

Keywords: grass-legume pastures; nutrient cycle; nitrogen uptake.

Abstract. Unground legume materials labelled with 15N were applied to the soil surface undera Rhodes grass pasture in south-eastern Queensland and the recovery of the applied 15N wasfollowed over periods of 1-3 years. Comparisons were made between two legumes,Macroptilium atropurpureum cv. Siratro and Desmodium intortum cv. Greenleaf, betweenleaf and stem materials of different nitrogen (N) concentrations (0.5-3.8% N), and betweenfresh and dried materials. After 1 year, 15N in the applied materials had decreased by 25-91%,and 7-25% was discovered in the Rhodes grass. Except for leaf material of Greenleaf, thesechanges showed a positive, non-linear relationship to the percentage of N (% N) in the appliedmaterials. The changes for leaves of Greenleaf were less than would be predicted from their %N. Drying Siratro leaves and stems before applying them to the soil surface did notsignificantly affect the above changes. For N-poor materials (0.5-1.8% N) applied at 380-1360g dry matter/m², uptake of 15N by Rhodes grass was greater in the second year than in the firstyear, whereas for N-rich materials (3.8% N) applied at 140 g dry matter/m² uptake of 15N inthe second and third years was only 23 and 12%, respectively of that in the first year.

48

Palm, C.A. and Sanchez, P.A. (1990): Decomposition and nutrient release patterns of theleaves of three tropical legumes. Biotropica 22:330-338.

Keywords: legumes; Cajanus cajan; Erythrina; Inga edulis; polyphenolics; Peru; nitrogen;alley cropping; lignin; soil organic matter; nitrogen cycle; legume trees; Amazon region;South America; mineralization; agroforestry; phosphorus.

Abstract. Information on decomposition and nitrogen release patterns of tropical legumes isscarce despite the important role of legumes in agroforestry systems. Decomposition patternsof the leaves of three tropical legumes Inga edulis Mart., Cajanus cajan (L.) Millsp., andErythrina sp. were determined by a litterbag study in an alley cropping experiment conductedin the Peruvian Amazon. The leaflets of the three species had similar nitrogen concentrationsbut different lignin and polyphenolic concentrations. Inga and Cajanus decomposed at similarrates (k = 0.91 and 1.72 yr-1, respectively) and had similar polyphenolic concentrations butdiffered in lignin. Erythrina had the lowest concentration of polyphenolics and decomposedthe fastest (k = 3.45 yr-1). Polyphenolics appeared to influence rates of decomposition morethan percent nitrogen or percent lignin. It is proposed that the polyphenolics bind to N in theleaves forming compounds resistant to decomposition. These compounds may be precursorsto stable forms of nitrogen in soil organic matter. Rates of nutrient loss followed the generaltrend potassium > phosphorus, nitrogen, and magnesium > calcium. It is apparent from thisstudy that not all leguminous leaves decompose and release nitrogen quickly, despite highnitrogen concentrations in the leaves. Nitrogen release by legumes with high polyphenolic

References 57

concentrations will be slower than that by legumes with low polyphenolic concentrations andhas important implications to nitrogen cycling and the selection of legumes for agroforestrysystems.

49

Balasubramanian, V. and Sekayange, L. (1991): Effects of tree legumes in hedgerows onsoil fertility changes and crop performance in the semi-arid highlands of Rwanda. BiologicalAgriculture and Horticulture 8:17-32.

Keywords: legume trees; Rwanda; manure; mulch; yields; beans; sorghum; maize; alleycropping; annual field crops; nutrient cycle; soil chemical properties.

Abstract. The soil fertility improvement potential of five tree legumes as alley hedges wasstudied on a Ultic Haplustox soil at a semi-arid highland site in Rwanda from 1983 to 1989.Tree species tested were C. calothyrsus Meissn., C. spectabilis DC, L. diversifolia (Lam.) deWit., L. leucocephala (Lam.) de Wit. and S. sesban (L.) Merr.; they grew to a height of 1.01 to2.15 m and 2.85 to 3.37 m, after 1 and 1.5 years respectively. S. sesban could not withstandintensive pruning (four times per year) and 83% of the trees died after six prunings. Incontrast, C. calothyrsus lost only 28%, both species of Leucaena 9 to 10%, and C. spectabilisnone of the trees after 18 prunings in 4.5 years. Above-ground biomass production increasedsteadily with the age of the trees. Mean values for 1984-89 were: 5.6 to 7.3 Mg/ha dry weightof leaf biomass and 3.7 to 5.0 Mg/ha of wood. Mean annual nutrient addition to soil throughleaf biomass was: 72 to 119 kg/ha of N, 2 to 3 of P, 47 to 94 of Ca, 8 to 19 of Mg, and 29 to60 of K, and it was equivalent to an application of 10 Mg/ha/year of cattle manure. Treemulch application reduced the rate of soil fertility decrease due to cropping; percent increasesover control were 2 to 20 for soil C, -3 to 7 for K, 4 to 51 for Ca, 7 to 31 for Mg, and 3 to 47for exchange capacity in mulched plots. Combined applications of leaf biomass and manureincreased the pH (water) by 0.4 to 0.5 units, K by 0 to 0.7 mmol, Ca by 10.8 to 17.6 mmol andMg by 0.5 to 2.3 mmol and exchange capacity by 10.5 to 34.0 mmol above the level of soilscleared from the savanna vegetation. Mean nutrient export from the site in woody stemsranged from 17 to 28 kg/ha/year of N, 1 to 2 of P, 13 to 16 of Ca, 2 to 5 of Mg, and 17 to 34of K. Grain yield increase of beans (Phaseolus vulgaris L.) and sorghum (Sorghum bicolor L.)to tree foliage application was the largest in C. spectabilis alleys, followed by the others. Cropyield increases due to tree mulch use were less in manured plots. Maize (Zea mays L.)response was poor. Tuber yield of sweet potato (Ipomoea batatas (L.) Lam.) decreased whenplanted in alleys, due to the lower tuber yield per unit crop area in alleys than in the controland a 14 to 32% yield fall off at the tree/crop interface.

50

Budelman, A. (1989): Effect of application of the leaf mulch of Gliricidia sepium on earlydevelopment, leaf nutrient contents and tuber yields of water yam (Dioscorea alata).Agroforestry Systems 8:243-256.

Keywords: mulch; Gliricidia sepium; Dioscorea alata; yields; nutrient cycle; legume trees;Africa.

Abstract. This paper describes the effects of the leaf mulch of Gliricidia sepium on thedevelopment and yield of Water Yam, Dioscorea alata. Using leaf mulch, the time taken forthe yam setts to sprout can be shortened by approximately 20 percent. Organic mulches


contain considerable quantities of plant nutrients. Increasing amounts of mulch improved theleaf nutrient contents of the yam crop and resulted in significantly higher tuber yields. Over atuber yield range up to c. 15 tons ha-1 each additional ton DM Gliricidia sepium mulch appliedresulted in a yield increment of about 2 ton yam tubers. A nutrient supply-nutrient extractionbalance is discussed, comparing mulch applied and yam tubers harvested. Mulching asagricultural technique is a useful and affordable tool in adapting low external input croppingsystems to local economic and environmental conditions.

51

Leach, G.J., Rees, M.C. and Charles-Edwards, D.A. (1986): Relations between summercrops and ground cover legumes in a subtropical environment. 2. Effects of sorghum andsunflower on the growth of Vigna trilobata and Medicago scutellata. Field Crops Research15:39-55.

Keywords: legumes; ground cover; Medicago scutellata; Sorghum bicolor; Helianthusannuus; erosion control; seed production; subtropics; Australia; yields; annual field crops;Vigna trilobata; erosion; seeds.

Abstract. Vigna trilobata (L.) Verdc. is a low growing legume with potential as a groundcover for controlling soil erosion in cropping lands of the subhumid/semi-arid subtropics ofnorthern Australia. When it was grown beneath sorghum (Sorghum bicolor (L.) Moench) andsunflower (Helianthus annuus L.) crops under well-watered conditions on a vertisol insouthern Queensland it decreased their yields by about 20% in the first season. This paperreports the effects of competition from crops sown at a normal dryland density or at half thenormal density on its growth. Vigna trilobata sown in pure stand in October produced 531 gm-2 of above-ground dry matter, and sown in January produced 323 g m-2, by the time thegrain crops sown at the same time were mature. Yields under mature sorghum sown at thenormal density (10 plants m-2) in October and January were 38% and 35% respectively ofthose from pure stands of ground cover sown at the same time. Under sunflower at the normaldensity (5 plants m-2), corresponding values were 42% and 22%. The decrease in dry matteryield attributable to competition for water, nutrients and/or radiation from the main crops wasproportional to the decrease in intercepted radiation. V. trilobata responded to shade in severalways, but a substantial increase in specific leaf area, together with some additionalpartitioning of dry matter to leaf, was sufficient to ensure that its leaf area index under cropswas similar to that in pure stands. Seed yields of 116 and 84 g m-2 were obtained from purestands of V. trilobata sown in October and January respectively. However, seed yields undercrops sown at the normal density were only 4-18% of those measured in pure stands. Seed sizewas not affected by treatment. We conclude that, under well-watered conditions in southernQueensland, V. trilobata grown as a ground cover under crops of sorghum and sunflowershould be able to produce sufficient biomass to decrease soil erosion, and also producesufficient seed for regeneration in successive seasons. Its growth and suitability are alsobriefly compared with those of an alternative ground cover legume, Medicago scutellata (L.)Mill. (snail medic).

References 59

52

Brockington, N.R., Stobbs, T.H., Newhouse, P.W. and Wadsworth, G.A. (1965): Theeffects of leys on soil fertility in the annual cropping areas of Uganda. Sols Africains 10:473-481.

Keywords: fertility; nitrogen; legumes; animal production; yields; ley farming.

Abstract. Evidence is presented that grazing resting land is beneficial to subsequent arablecrops. Organic carbon and total soil nitrogen are built up in the ley phase of the rotation anddecline with cultivation. Addition of inorganic nitrogen and the inclusion of legumes in theley greatly increase animal production but may depress the yields of following arable crops.This depression is commonly alleviated by the addition of single superphosphate and may bedue to imbalance of plant nutrients.

53

Toledo, J.M. and Serrão, E.A.S. (1982): Pasture and animal production in Amazonia. In:Hecht, S.B. (ed.), Amazonia: Agriculture and land use research. Cali (Colombia): CIAT(Centro Internacional de Agricultura Tropical), p. 281-309.

Keywords: Amazon region; nutrient cycle; phosphorus; fertilization; cattle; degradation;pasture management; tropical forest; sustainability; pastures.

Abstract. This paper presents some results of research conducted on pasture and animalproduction in the Amazon region. Soils in the Amazon basin are heterogenous, although mostare acid, deficient in P, have low base saturations and high Al levels. Land use potential forforestry, cattle ranching, agriculture and plantations should be evaluated according to soilconditions before developing settlement programs. In tropical rain forest ecosystems, mostmineral nutrients are stored in biomass and detritus, and only to a smaller amount in the soil.Effective nutrient cycling, mainly between biomass and detritus, minimizes nutrient lossesfrom the system. The authors suggest that well-managed pastures or plantations couldmaintain soil fertility in a similar way, and propose a model of sustainable pasture and animalproduction for rain forest areas. This model includes different methods of forest clearingaccording to local conditions and avoiding excessive soil compaction, and the establishmentof pastures after a cropping period. Pastures should be adapted to soil conditions, consist ofgrass-legume associations and must be maintained by management measures such as liming,phosphorus fertilization and adequate stocking rates. Adapted cattle or buffalo breeds shouldbe selected. The high potential of Amazonia for cattle production, compared with nativesavanna or cerrado pastures, is emphasized. (Abstract by bibliography authors)

54

Bolan, N.S., Hedley, M.J. and White, R.E. (1991): Processes of soil acidification duringnitrogen cycling with emphasis on legume based pastures. Developments in Plant and SoilScience 45:169-179.

Keywords: nitrogen; legumes; pastures; nitrogen cycle; fertilization; nitrogen fixation;minerali-zation; soil acidity; soil chemical properties; pollution; leaching.

Abstract. In areas that remain unaffected by industrial pollution soil acidification is mainlycaused by the release of protons (H+) during the oxidation of carbon (C), sulphur (S) and


nitrogen (N) compounds in soils. In this review the processes of H+ ions release during Ncycling and its effect on soil acidification are examined. The major processes leading toacidification during N cycling in soils are: (i) the imbalance of cation over anion uptake in therhizosphere of plants either actively fixing N2 gas or taking up NH4

+ ions as the major sourceof N, (ii) the net nitrification of N derived from fixation or from NH4

+ and R-NH2 basedfertilizers, and (iii) the removal of plant and animal products containing N derived from theprocess described in (i) and losses of NO3

− -N by leaching when the N input form is N2,NH4

+ or R-NH2. The uptake of excess cations over anions by plants results in the acidificationof the rhizosphere which is a "localized" effect and can be balanced by the release of hydroxyl(OH-) ions during subsequent plant decomposition. Nitrification of fixed N2 or NH4

+ and R-NH2 based fertilizers, and loss of N from the soil either by removal of products or by leachingof NO3

− -N with a companion basic cation, lead to 'permanent' acidification.

55

Bromfield, S.M., Cumming, R.W., David, D.J. and Williams, C.H. (1983): Change in soilpH, manganese and aluminium under subterranean clover pasture. Australian Journal ofExperimental Agriculture and Animal Husbandry 23:181-191.

Keywords: degradation; fertilization; legumes; soil acidity; soil chemical properties;sustainability.

Abstract. Changes in soil pH, manganese and aluminium as a result of long periods undersubterranean clover pasture were examined in soils formed on granite, basalt and sedimentaryrocks near Goulburn, New South Wales. Decreases in pH of yellow duplex soils formed ongranite, sedimentary rocks and basalt had occurred to depths of 60, 40 and 30 cm,respectively. The smaller depth of acidification in the latter two soils is considered to be dueto their shallower A horizons over well buffered, clay B horizons. Under the oldest pastures(55 years) the decreases exceeded one pH unit throughout the entire sampled depth (60 cm). Insome soils, under old improved pastures, calcium chloride-extractable manganese hadincreased to more than 20 ppm throughout the 60 cm profile and to greater than 50 ppm in thesurface 10 cm. These levels are considered toxic to sensitive plant species and the highestlevels may be toxic to subterranean clover. The amounts of extractable manganese in soilsappear to be determined by both pH and the amounts of reactive manganese. In general, theamounts of total and reactive manganese were appreciably higher in the soils of basalticorigin. Substantial increases in extractable and exchangeable aluminium had alsoaccompanied the decrease in pH and, in the surface 10 cm, were greatest in the soils formedon sedimentary parent materials. In many of the soils under old improved pastures,exchangeable aluminium, as a percentage of the effective cation exchange capacity, nowexceeds 12%, especially in the 5-10 cm layer, and is probably harmful to sensitive species.Increases in exchangeable aluminium also occurred below the surface 10 cm and, in thegranitic soils under the oldest pastures, exchangeable aluminium accounted for 30-50% of theeffective cation exchange capacity throughout the 5-50 cm soil depth. The adverse changes inpH, manganese and aluminium observed in this study can be expected to continue under manyimproved pastures and to generate soil conditions unsuitable for many agricultural plants. Theuse of lime to arrest or reverse these changes seems inevitable.

References 61

56

Williams, J. and Chartres, C.J. (1991): Sustaining productive pastures in the tropics. 1.Managing the soil resource. Tropical Grasslands 25:73-84.

Keywords: pastures; tropics; Australia; sustainability; degradation; soil chemical properties;soil acidity; soil salinity; deforestation; legumes; erosion control; watershed; grassland; trees;soil biology.

Abstract. The grazing of pasture systems has many of the elements essential to a sustainableagro-ecosystem wherein the soil resource is not degraded through time. Unfortunately there isincreasing evidence that the soils of Australian tropical grasslands are suffering serious andpermanent degradation through our inability to manage grazing pressure under the highlyvariable climatic regime which characterizes the Australian tropics. This paper details theevidence of soil degradation under our current rangeland management and illustrates how farthese practices are from that of a sustainable system. The challenge to find grazing systemsthat are sustainable is shown to lie in recognizing that the soil-plant-animal ecosystem must bestudied in an integrated way. Focus on short term animal productivity without consideration ofthe consequences to all other essential components of the ecosystem is shown to be a primarycause for degradation of the soil resource. Too often the consequences of a practice have notbeen considered because the components of the agricultural system have been studied inisolation. Both salinity and soil acidification are identified as soil resource management issuesthat must receive attention in the Australian tropics. The use of tropical legumes, the clearingof woodlands, and the use of introduced grasses are all managements that can radically alterthe flux of water, nutrient and salt in the soil profile. The management of these factors is thekey to control of both salinity, and soil acidification. The place and balance of the grass,legume, shrub and tree is fundamental. Progress in building sustainable grazing systems in thetropics requires integrated ecological studies with increasing emphasis of both the role of soilbiology in the cycling of nutrients and the movement of water and solute in the system.

57

Cumming, R.W. (1991): Long-term effects of lime in extensive pasture areas of Australia.Developments in Plant and Soil Science 45:453-464.

Keywords: pastures; Australia; soil acidity; soil chemical properties; sustainability.

Abstract. Acid soils treatment in Australia, is an important part of extensive pasture and cropmanagement systems. Under old improved pastures, calcium chloride-extractable manganese(Mn) and aluminium (Al) have increased to levels which restrict plant growth. Alternativetreatments, using both topdressed and surface incorporated lime, have shown positive effectson the CaCl2 extractable Mn and Al. Soil profiles from limed and unlimed pastures weresampled at 2 cm intervals to 20 cm depths, following single applications of lime 10 years ago.Aluminium was reduced by 100% (from 14.5 ppm Al) at the soil surface to 35% at 20 cm ingranitic derived soils. In a less acidic basalt derived soil, a 100% reduction has been obtainedto 20 cm (from 8.7 ppm Al). Manganese was reduced between 32.5% and 76% in the granitesoils (from 12.6 ppm Mn) with basaltic soils having a 62% to 97% reduction in manganeselevels (from 23.6 ppm Mn). Long term reduction in these toxic elements, has been mirroredby permanent changes in soil pH and changes in the exchangeable cations, particularlycalcium, in a long term agronomic trial.


58

Ridley, A.M., Slattery, W.J., Helyar, K.R. and Cowling, A. (1990): Acidification undergrazed annual and perennial grass based pastures. Australian Journal of ExperimentalAgriculture 30:539-544.

Keywords: grasses; pastures; soil acidity; carbon cycle; leaching; grass-legume pastures; soilchemical properties; Australia; sustainability.

Abstract. Soil samples to a depth of 60 cm were collected from adjacent, 39-year-old,phalaris-based and annual pasture fields on an acid soil at Rutherglen, north-eastern Victoria.The fields had similar histories of fertilizer application and stock enterprise. Minimum netacid addition rates were determined under both pasture types, and the soil under annualpasture showed greater acidification. Carbon cycle acid addition contributed 1.31 and 1.36kmol H+/ha and year to net acid addition on annual and phalaris pastures, respectively.Because slow alkaline soil reactions in the field contribute to buffering capacity on an acidsoil and lead to underestimation of net acid addition rate and nitrate leaching, estimates ofsuch reactions were made for both pasture types. If correct assumptions were used nitrateleaching was substantial under both pasture types but was reduced by 1.01 kmol H+/ha andyear under phalaris pasture. This suggests that perennial grass based pastures can be used toreduce acidification on pastoral soils. Alkali addition to counteract net acidification may benecessary on acid soils to maintain management options for growing aluminium-sensitivespecies.

59

Ridley, A.M., Slattery, W.J., Helyar, K.R. and Cowling, A. (1990): The importance of thecarbon cycle to acidification of a grazed annual pasture. Australian Journal of ExperimentalAgriculture 30:529-537.

Keywords: carbon cycle; pastures; soil acidity; sheep; stocking rate; nitrogen cycle; Australia;production level; fertilization; nitrogen.

Abstract. Soil samples to a depth of 60 cm were collected from 3 fields of a 73-year-oldexperiment in north-eastern Victoria. One field (unfertilized) had never received fertilizer,whereas, the other two fields (fertilized) had received 4.5 t/ha superphosphate. One of thefertilized fields also had a lime application history (fertilized and limed). The fields wereparticularly useful for estimation of the amount of acid added by the carbon cycle as recordsof lamb, wool and hay removal over a long period were available. The soil pH of the fertilizedfield had declined relative to the unfertilized field to a depth of at least 30 cm. The fieldreceiving fertilizer and lime had a similar pH profile to that of the unfertilized field. Pastureimprovement resulted in much higher stocking rates and consequent product removal (hay,wool and meat) from the fertilized and limed fields compared with the unfertilized field (68,72 and 12 kmol H+/ha, respectively). Carbon and nitrogen cycle acidification accounted for 65and 35%, respectively, of the net acid addition on the fertilized field. The acidification ratesfor the fertilised, fertilised and limed, and unfertilized fields over the 73-year period were1.42, 2.37 and 0.16 kmol H+/ha and year. These acid addition rates are likely to beunderestimated because the laboratory pH buffering capacity method used did not account forslow buffering reactions in the field.

References 63

60

Coventry, D.R. (1992): Acidification problems of duplex soils used for crop-pasturerotations. Australian Journal of Experimental Agriculture 32:901-914.

Keywords: Australia; pastures; yields; ley farming; soil chemical properties; soil acidity;degradation.

Abstract. The acidification of duplex soils used for crop-pasture rotations has been reportedwidely in Australia in the winter dominant rainfall regions. At some locations induced soilacidity limits crop and pasture yield. The rate of soil acidification is affected by soilproperties, agricultural management and rainfall. Rates of acid addition of 0.6-6 kmol H+/haand year have been measured from long-term crop-pasture rotation experiments; these ratesare comparable with values reported from pastoral studies in higher rainfall areas.Components of both the carbon and nitrogen cycles contribute to this acid addition, with lossof nitrate-nitrogen below the rooting depth of these predominantly annual plant systems likelyto be the main cause of acidification. Lime application has been recommended as a means ofcorrecting acidification and improving crop and pasture yield. There is little information onthe longevity of any beneficial effects of lime, the movement of lime in the soil and re-acidification of the soil in crop-pasture systems. A long term experimental site with rotation,deep tillage and lime treatments has been soil sampled throughout a 9-year period for changesin soil pH and aluminium. Soil pH decreased with increasing time after lime application. Atlower lime rates (0.5-1.0 t/ha) there was no difference in pH or exchangeable Al after 9 years,compared with the unlimed soil. At the higher lime rates there was downward movement ofthe neutralizing effect of lime with time, as well as acidification of the soil. However, theyield responses obtained with all of the lime rates were maintained 9 years after 1 applicationof lime, even though the soil was strongly acid according to the measures used. Strategies forcountering soil acidification may require an initial application of lime if acidity factors arerestricting yield. Management systems which increase the permeability of the B horizon ofduplex soils and which promote plant growth and a deep root system are essential forcountering acidity in a crop-pasture rotation.

61

Diez, J.A., Polo, A., Cerri, C.C. and Andreux, F. (1991): Influência do pousio e dapastagem sobre a dinâmica de nutrientes em oxissolos recentemente desflorestados naAmazônia Oriental (Influence of fallow and of pasture on the nutrient dynamics in recentlydeforested Oxisols of Eastern Amazonia). Pesquisa Agropecuária Brasileira 26:77-83.

Keywords: fallow; pastures; Oxisols; deforestation; nitrogen; fertility; burnings; soil pH; Aldecrease.

Abstract. The present paper deals with the effects of six and eight years of fallow and of nineyears of cultivated pasture, on nutrient dynamics in deforested Oxisols of Eastern Amazonia.Electroultrafiltration (EUF) method was used, in order to propose efficient systems to improvesoil fertility in this area. Forest burning brought about immediate increase of soil pH, whereassubsequent decrease in extractable EUF-Al and increase in exchangeable K and Ca werenoticed. Pasture installation after deforestation has shown appreciable prospect to maintain anadequate level of soil fertility since it increases pH and reduces the EUF-Al content. Ascompared with the soil left under fallow for eight years, higher pH values, lower amount of


extractable Al, higher amounts of mobile P and K, higher biological soil activity, and stableamounts of available nitrogen were observed in the pasture soil.

62

Williams, J. (1991): Search for sustainability: Agriculture and its place in the naturalecosystem. Agricultural Science 4:32-39.

Keywords: sustainability; ecosystems; degradation; Australia; farming systems; nutrient cycle;soil erosion; soil salinity.

Abstract. Extensive land degradation in rural Australia is testimony to the fact that currentfarming systems are not sustainable. The current practices are both mining the reservoir ofnutrients and carbon as well as perturbing the ecological and hydrological balances of ourlandscapes. Land degradation is so often the result of a failure to examine the whole farmingsystem in the context of the hydrological or nutrient cycle in which it is cast. Progress towardssustainable agricultural practices will only be made while the implications of these practicesare viewed and examined as part of the regional ecosystem. Agricultural scientists and thefarming community must think beyond the farm gate to see how the farm is integrated withthe catchment and the landscape as a whole.

63

Angers, D.A. (1992): Changes in soil aggregation and organic carbon under corn and alfalfa.Soil Science Society of America Journal 56:1244-1249.

Keywords: soil physical properties; soil organic matter; maize; fallow; Medicago sativa.

Abstract. Data on rates of changes in soil structure and organic matter under differentcropping systems are necessary for the development of soil and water conservation strategies.Changes in C content and waterstable aggregation of a Kamouraska clay (fine, mixed, frigidTypic Humaquept) under continuus silage corn (Zea mays L.) and an alfalfa (Medicago sativaL.) stand were monitored monthly during five consecutive growing seasons. A bare soil(fallow) was included as a control. Under alfalfa, the mean weight diameter (MWD) of water-stable aggregates increased from 1.5 to 2.3 mm during the 5-yr period. An asymptoticregression explained 69% of the variation in MWD with time under alfalfa. This increase inMWD was largely attributed to an increase in aggregates >2 mm at the expense of theaggregates of 0.25 to 1.0 mm diameter. Also, under alfalfa, the C content increased followinga sigmoidal shape from 26 g kg-1 in the first season to 30 g kg-1 in the last year. Changes inMWD were comparatively larger and took place more rapidly than those in C. A correlationcoefficient of 0.74** (significant at the 0.01 probability level) was obtained between C andMWD. Under corn and fallow (bare-soil control), changes in the MWD and C content wereminimal during the 5 yr. About one half of the temporal variation in MWD under corn andfallow could be explained by the variation in soil water content at time of sampling.Conversely, the absence of a significant relationship between water content and MWD underalfalfa suggests that the soil aggregates under this treatment were not subject to slaking.

References 65

64

Budelman, A. (1989): The performance of selected leaf mulches in temperature reduction andmoisture conservation in the upper soil stratum. Agroforestry Systems 8:53-66.

Keywords: mulch; Leucaena leucocephala; Gliricidia sepium; Flemingia macrophylla;legume trees; soil physical properties.

Abstract. This paper reports on the effect of the leaf mulches of Leucaena leucocephala,Gliricidia sepium and Flemingia macrophylla on moisture content and temperature in the first5 cm of the soil. The mulches were applied at a standard quantity of 5000 kg ha-1 DM. Inorder to characterise a mulch material two parameters are distinguished: the initial impact (Ii)and the effective lifetime (Te) of a mulch material. I is expressed in terms of percentagesurplus moisture or degrees Celsius average temperature reduction. T quantifies the durationof the effect. Of the three mulch materials that of Flemingia macrophylla performs best interms of moisture retention and lowering soil temperatures as well as in terms of longevity ofthe effect. Leucaena leucocephala mulch shows the smallest impact, over the shortest period.

65

Pereira, H.C., Chenery, E.M. and Mills, W.R. (1954): The transient effects of grasses onthe structure of tropical soils. Empire Journal of Experimental Agriculture 22:148-160.

Keywords: grasses; crop rotation; Paspalum notatum; cover crops; Pueraria phaseoloides;infiltration; pore-space; Chloris gayana; soil structure.

Abstract. A detailed study was made of the differences in soil structure in a crop-rotationexperiment on a tropical soil. Two different techniques of soil sieving were compared withvolumetric measurements of pore-space, and with percolation and rainfall-acceptance tests onsoil cores. Three grass species (Pennisetum purpureum, Paspalum notatum, Chloris gayana),three cover crops (Pueraria phaseoloides, Ipomoea batatas, Leucaena glauca), and threecultivated crops (Arachis hypogaea, Crotalaria juncea, Manihot utilissima) were each growncontinuously for 3 years. All treatments were then given one year of intensive uniformcropping before the structure comparisons were made. The two tests for water-stableaggregation showed serious discrepancies, but they both agreed with the remaining tests inshowing general differences between the groups of treatments after grass rest and those aftercontinuous cultivation. Rainfall infiltration rates were comparatively low after only one yearof arable cropping, indicating a rapid loss of the benefits built up under a grass rest. A similarset of tests, on adjacent areas of a rotation on a lateritized volcanic clay, showed even morerapid loss of physical structure after the breaking of grass. These results illustrate the need tomeasure rates of run-down as well as build-up of soil-structure, and the desirability of usingphysical tests more realistic than wet sieving.

66

Frost, W.E. and Edinger, S.B. (1991): Effects of tree canopies on soil characteristics ofannual rangeland. Journal of Range Management 44:286-288.

Keywords: trees; grassland; soil physical properties; soil chemical properties; California.

Abstract. In the central California region of annual rangeland, herbage production beneathblue oak (Quercus douglasii Hook & Arn.) canopies is greater and production beneath the


canopies of interior live oak (Quercus wislizenii DC) and digger pine (Pinus sabinianaDougl.) is less than that in adjacent open grassland. The objective of this investigation was toassess the impact of these major overstory species on soil-associated characteristics in aneffort to explain this tree-herbage production relationship. Greater amounts of organic carbon(OC), greater cation exchange capacity (CEC), lower bulk density, and greater concentrationsof some nutrients were found beneath blue oak canopies than in open grassland. This explains,at least in part, the increased herbage production beneath blue oak canopy.

67

Lal, R., Wilson, G.F. and Okigbo, B.N. (1978): No-till farming after various grasses andleguminous cover crops in tropical Alfisol. I. Crop performance. Field Crops Research 1:71-84.

Keywords: grasses; cover crops; soil properties; mulch; Nigeria; Panicum maximum; legumes;Centrosema pubescens; Pueraria phaseoloides; Brachiaria; Stylosanthes guianensis; maize;cowpea; Cajanus cajan; soybeans; cassava; nitrogen; soil physical properties; infiltration; soilbulk density; earthworms; yields; Glycine wightii; Melinis minutiflora.

Abstract: The effects of four grasses and four leguminous cover crops on soil properties, andon the applicability of zero-tillage technique for arable crop production with killed sod mulch,was investigated on tropical Alfisol near Ibadan, Nigeria. The cover crops consisted of fourgrasses, Panicum maximum, Setaria sphacelata, Brachiaria ruziziensis, and Melinisminutiflora, and four legumes, Centrosema pubescens, Pueraria phaseoloides, Glycinewightii, and Stylosanthes guianensis. Two years after establishing cover crops, arable cropswere planted through chemically killed sod. The arable crops grown were maize (Zea mays),cowpea (Vigna unguiculata), pigeonpeas (Cajanus cajan), soybeans (Glycine max), andcassava (Manihot esculenta). Cover crops had a significant effect on soil chemical andphysical properties. Organic carbon, total nitrogen, and CEC were higher under Melinisminutiflora, Glycine wightii, Centrosema, and Pueraria than with control and other covercrops. There were differences between cover crops in soil physical properties. Infiltration rateand soil bulk density were generally low under cover crops compared with control. Earthwormactivity was related to the quantity and persistence of killed sod mulch under various covercrops. Maximum soil temperature under killed sod mulch was as much as 10°C lower than incontrol. Soil moisture storage was affected both by mulch cover and by the canopy cover ofthe arable crop grown on the killed sod. Soil moisture storage was generally high under killedsod mulch compared with control. There were significant differences in arable crop yieldbetween various cover crops. Significantly higher crop yields were obtained underCentrosema, Pueraria, Stylosanthes, and Brachiaria than with control and other cover crops.Brachiaria sod was, however, difficult to eradicate and to plant in with zero-tillage technique.Maize and cowpea grain yield and cassava tuber yield were positively related to infiltrationrate and negatively to soil bulk density.

68

Vera, R.R., Thomas, R., Sanint, L. and Sanz, J.I. (1992): Development of sustainable ley-farming systems for the acid-soil savannas of tropical America. Anais, Academia Brasileira deCiências 64:105-125.

References 67

Keywords: ley farming; livestock; economics; Brazil; Colombia; pastures; rice; grasses;legumes; acid soil; Venezuela; sustainability; savanna.

Abstract. The paper reviews the evolution of the agricultural and livestock sectors in theneotropical savannas of Latin America, and their contribution to economic development andhuman nutrition. It is shown that the savannas are responsible for an increasing share of totalagricultural production in Brazil, Colombia and Venezuela. The natural resources of thesesavanna lands are discussed, with emphasis on the physico-chemical characteristics of the soil,and the constraints that they impose on crop and pasture production. The development of acid-soil tolerant crops and forages is briefly summarized. Mechanisms of adaptation are described,and the contribution of adapted germplasm to soil enhancement is discussed. Lastly, the paperreviews studies conducted in Colombia to research crop-pasture integration in tropical ley-farming systems, using selected adapted rice lines and grass and legume forages asexperimental models. Evidence collected over four consecutive years clearly shows thetechnical feasibility of developing alternative systems that combine annual crops and grazedpastures using low external inputs and enhancing soil characteristics. Ex-ante economicanalysis reveal that these systems are also highly profitable.

69

King, K.L., Greenslade, P. and Hutchinson, K.J. (1985): Collembolan associations innatural versus improved pastures of the New England Tableland, NSW: Distribution of nativeand introduced species. Australian Journal of Ecology 10:421-427.

Keywords: improved pastures; pastures; Collembola; introduced species; Australia;phosphorus; soil fauna; biodiversity; species diversity.

Abstract. Native Australian species of Collembola dominated natural pasture in numbers ofspecies present and in abundance, while introduced Collembola dominated fertilized pasturesown to exotic species. Those collembolan species which were restricted to one pasture typeonly were mainly epigeal and hemiedaphic species of the herbage and litter. Increased grazingby sheep decreased species richness and increased uniformity of Collembola in both pasturetypes. The abundance of introduced Collembola was positively associated with phosphoruscontent of litter.

70

Curry, J.P. (1987): The invertebrate fauna of grassland and its influence on productivity. 1.The composition of the fauna. Grass and Forage Science 42:103-120.

Keywords: grassland; invertebrates; soil fauna; soil biomass.

Abstract. The invertebrate groups which are of most significance in grassland are brieflyreviewed. Factors influencing the abundance and composition of the fauna are consideredtogether with the types of damage caused in grassland, the economic importance of suchdamage and beneficial effects on soil fertility.

71

Rushton, S.P. (1988): Earthworms in pastoral agriculture. Outlook on Agriculture 17:44-48.


Keywords: earthworms; pastures; soil chemical properties; soil physical properties; grassland;fertilization; pasture management; soil biology.

Abstract. It is well known that earthworms of various species, with widely differing feedingand burrowing habits, can have a considerable effect on the structure and composition of theupper levels of the soil. It is, however, often difficult to relate these effects to soil fertility inparticular situations and to manipulate worm populations to produce beneficial results.

72

Baker, G., Buckerfield, J., Grey-Gardner, R., Merry, R. and Doube, B. (1992): Theabundance and diversity of earthworms in pasture soils in the Fleurieu Peninsula, SouthAustralia. Soil Biology and Biochemistry 24:1389-1395.

Keywords: pastures; Australia; earthworms; soil chemical properties; species diversity;nitrogen.

Abstract. Earthworms were surveyed in 113 pasture soils in the Mount Lofty Ranges, FleurieuPeninsula, South Australia, in a region where annual rainfall is 600-1200 mm and the climateis mediterranean. The soils within these pastures included a variety of profile forms (e.g.sandy soils with yellow, brown or red clays in the B horizon; uniform coarse textured sands).The most widespread earthworm species were Aporrectodea trapezoides (found at 95% ofsites), Microscolex dubius (61%), Aporrectodea rosea (38%) and Aporrectodea caliginosa(36%). These are all introduced species. The total densities of earthworms varied from 0 to608 m-2 (mean = 169.2). At most sites (66%), densities were < 200 m

-2. Native earthworms

were present at 40 sites but their total densities exceeded 100 m-2 at only 7 sites. The speciesrichness and diversity of the earthworm communities were low; never more than 5 specieswere found in any one pasture (mean = 3.1). The abundance of the introduced species (allspecies combined) varied between soil profile forms, being least in the uniform sands. Nosuch variation was found for native species. Several significant, but weak, correlations wereobtained between the numbers and weights of earthworms and other environmental variables(e.g. rainfall, depth of A horizon, % sand, clay, nitrogen and carbon). Stepwise multipleregression of the numbers and weights of introduced species against these environmentalvariables suggested that % clay was the most important regressor. The potential for increasingthe abundance and diversity of earthworms in Australian soils is discussed.

73

Knight, D., Elliott, P.W., Anderson, J.M. and Scholefield, D. (1992): The role ofearthworms in managed, permanent pastures in Devon, England. Soil Biology andBiochemistry 24:1511-1517.

Keywords: earthworms; pastures; denitrification; mineralization; leaching; nitrogen; England;fertilization; cattle; hydrology.

Abstract. Studies were carried out on experimental pasture plots which are drained orundrained and receiving 0, 200 and 400 kg N ha-1 yr-1 as inorganic fertilizer. Earthwormpopulations (dominated by Lumbricus rubellus and Aporrectodea caliginosa) were lowest(71.0 ±11.4 g m-2) on the undrained 0N plots and highest (100.3 ±13.4 g m-2

) on theundrained 200N plots. Deep burrowing species appear to be excluded from colonizing thedrained plots by the high water-table during winter and spring. Aggregations of earthworms

References 69

beneath dung pats were recruited laterally peaking at a population equivalent of 417.5 ±60 gm-2

after 63 days. Local burrowing activities resulted in increased macroporosity over a periodof 105 days. Earthworm casts were found to have 3-5 times higher denitrification rates thansurrounding soil with lower endogenous rates of N2O production. Denitrification wasdetermined by cast NO3

− -N content and fertilizer applications. Earthworm casts may make asignificant contribution to the heterogeneity associated with field measurements ofdenitrification. Lysimeter studies were also carried out using soil monoliths to investigate theeffects of earthworms (including Lumbricus terrestris) on nutrient leaching from treatmentsreceiving the equivalent of 200 kg N ha-1 as cattle slurry or inorganic fertilizer. Nitrateconcentrations in leachates were low in the unfertilized treatments but earthworms increasedlosses three times. Nitrate losses were higher in the slurry treatments, possibly because ofdamage to the sward, with proportionally smaller earthworm effects. It is concluded that themoderate population densities of surface active species still have detectable effects on thehydrology and mineral N fluxes in intensively managed pastures although their effects onsward production are negligible in relation to the main plot treatments. Earthworm activitymay be an important determinant of heterogeneity in the rates of soil processes.

74

Serrão, E.A. and Toledo, J.M. (1990): The search for sustainability in Amazonian pastures.In: Anderson, A.B. (ed.), Alternatives to deforestation: Steps toward sustainable use of theAmazon rain forest. New York: Columbia University Press, p. 195-214.

Keywords: sustainability; Amazon region; tropical forest; pasture management; fertilization;nutrient cycle; degradation; insect pests; fungal diseases; agroforestry; adapted germplasm.

Abstract. In the past three decades, cattle ranching has become a major source of deforestationin the Amazon Basin, largely as a consequence of government incentives that have proved tobe both ecologically and socioeconomically dubious. It is currently estimated that at least tenmillion hectares of forest have been converted to highly unstable pastures, of which about 50percent are now in advanced stages of degradation. In this essay, we emphasize the need toreduce the rate of forest clearing for cattle ranching by increasing the longevity of still-productive pastures and by reclaiming those pastures that have been severely degraded. Thispaper 1) examines nutrient cycling in pasture ecosystems as a basis for sustainability; 2)describes the causes of biotic instability in pastures during their first and subsequent cycles; 3)outlines present and potential technologies for increasing pasture stability and for reclaimingdegraded sites; 4) analyzes the potential of low-cost technology based on newly adoptedgermplasm of grasses and legumes for open pastures and agrosilvopastoral systems; and 5)suggests research priorities for intensifying land management and increasing pasture sustain-ability.

75

Hecht, S.B. (1982): Agroforestry in the Amazon Basin: Practice, theory and limits of apromising land use. In: Hecht, S.B. (ed.), Amazonia: Agriculture and land use research. Cali(Colombia): CIAT (Centro Internacional de Agricultura Tropical), p. 331-371.

Keywords: agroforestry; erosion control; sustainability; Amazon region; nutrient cycle;tropical forest; shifting cultivation; deforestation; forage trees; cattle; pest control.


Abstract. This paper explores the potentials for agroforestry in the Amazon Basin anddescribes already established forms of this land use system in the region. The latter includecombinations of commercial timber trees with annual food crops or with cocoa and coffeeplantations; furthermore, existing silvopastoral systems, such as pastures under native orintroduced timber trees, rubber trees, oil palm, fruit and nut producing trees or forage trees arediscussed. Information is given about woody species of commercial interest as sources oftimber, forage, oils, resins and medicinals. The importance of agroforestry for soilamelioration, erosion control, pest dynamics and efficient nutrient cycling, thus sustainabilityof the agricultural system as a whole, is outlined. The author emphasizes that the expansion ofagroforestry in Amazonia is limited only in part by lack of technical experience. Landconflicts, the view that dramatic physical alteration of a landscape is a proof of ‘progress’ andthe speculative character of land ownership interfere with a rational resource use in theAmazon region. (Abstract by bibliography authors)

76

Buschbacher, R.J. (1987): Deforestation for sovereignty over remote frontiers; case studyNo. 4: Government sponsored pastures in Venezuela near the Brazilian border. In: Jordan,C.F. (ed.), Amazonian Rainforests: Ecosystem disturbance and recovery; Ecological Studies60. New York: Springer Verlag, p. 46-57.

Keywords: deforestation; nutrient cycle; Amazon region; phosphorus; Brachiaria decumbens;degradation; shifting cultivation; soil chemical properties; South America; tropical forest;pastures.

Abstract. Nutrient cycling and net primary productivity were investigated in an undisturbedrain forest site and two adjacent pasture sites under grazing conditions in the Amazon regionnear San Carlos, Venezuela. One of the pasture sites under investigation followed natural rainforest vegetation, whereas the other one had been a secondary forest following shiftingcultivation. Both had simultaneously been cleared and burned, and a Brachiaria decumbenspasture was established without any fertilizer input. After pasture establishment, changes inthe total nutrient stocks and particularly in the distribution of nutrients between ecosystemcomponents were observed. In general, nutrient stocks in the living biomass decreased, whilesoil nutrient levels increased. The most important difference between pasture derived fromprimary forest and that from secondary forest was in the level of soil nutrients at the initiationof grazing, being much lower in the pasture from secondary forest than in the pasture formedfrom mature rain forest. The amount of available phosphorus in the soil increased afterburning, but decreased quickly after 1 year in pasture. Total above-ground net primaryproductivity of the pasture formed from primary forest was very close to that of theundisturbed rain forest and was maintained during the three years under investigation. Above-ground net primary productivity in the pasture derived from secondary forest was about 50-60% of that derived from primary forest. The lower productivity was probably due to lowerlevels of calcium, potassium and magnesium in the secondary forest pasture. Furthermore,problems of animal production due to mineral deficiencies and possible restrictions toresilience of forest on abandoned pastures are discussed. (Abstract by bibliography authors)

References 71

77

Luizão, R.C.C., Bonde, T.A. and Rosswall, T. (1992): Seasonal variation of soil microbialbiomass – the effects of clearfelling a tropical rainforest and establishment of pasture in thecentral Amazon. Soil Biology and Biochemistry 24:805-813.

Keywords: pastures; deforestation; tropical forest; Brachiaria humidicola; nitrogen cycle;mineralization; Amazon region; soil biomass; nitrogen.

Abstract. The effects of clearfelling a tropical rainforest and establishing pasture on soilmicrobial biomass and nitrogen transformations were assayed monthly over 1 yr in threeadjacent systems in the central Amazon region; (1) virgin rainforest; (2) slashed-and-burntforest; and (3) recently established pasture. The amounts of soil organic matter (SOM) andsoil microbial biomass-carbon (biomass-C) were substantial in all systems. Total soil-Cranged between 1.9 and 5.2% depending on management and soil layer, whereas biomass-Cranged between 3.5 and 5.3% of total soil-C. The soil biomass-C decreased upon slashing-and-burning to 64% of its original value (1287 micrograms/g) in the forest (0-5 cm soil layer)and increased after establishment of pasture to 1290 micrograms/g, but remained unchangedin the deeper 5-20 cm soil layer. No significant seasonal variation was measured in any systemor soil layer. Soil respiration responded to management like microbial biomass-C but variedsignificantly over the season with the smallest respiration found in the driest month (October)and the largest respiration at end of the rains in May. Pools of mineral N varied considerablyin all systems and soil layers and displayed identical seasonal variations. The forest topsoilcontained the highest amounts (on average 47 micrograms N/g) and the pasture soil thesmallest amounts (on average 24 micrograms N/g). The transition of the forest ecosystem to apasture resulted in increased NO3

− concentrations. Net N-mineralization and net NO3−

production monitored during short-term laboratory incubations were used as indices of Nmineralization and nitrification. No significant differences in N-mineralization indices weremeasured between systems, but substantial within season variations were recorded in allsystems and soil layers. The variations were synchronized in time with extreme net N-mineralization in September and net N- mineralization in October. Significant nitrificationindices were measured in all systems. They were identical in the systems, except for smallindices found in topsoil of the slashed and burnt area, where, on the other hand, certainlocalized areas with extreme nitrification rates were detected.

78

Eden, M.J., Furley, P.A., McGregor, D.F.M., Milliken, W. and Ratter, J.A. (1991): Effectof forest clearance and burning on soil properties in northern Roraima, Brazil. Forest Ecologyand Management 38:283-290.

Keywords: Brazil; tropical forest; Panicum maximum; grasses; Amazon region; deforestation;soil chemical properties; soil physical properties; cattle; degradation; Brachiaria humidicola;pastures.

Abstract. Clearance of evergreen seasonal forest for cattle pasture was examined at a ranch130 km NW of Boa Vista. Colonião (Panicum maximum) and kikuyu grass (Brachiariahumidicola) are commonly established on cleared forest land. Current rates of clearance arerather low as also is grazing intensity (1-2 animals/ha), but soil physical and chemical changesare occurring. Topsoil bulk density is increasing over time in new pastures; and availablenutrients decrease from the enhanced levels that prevail after initial clearance and burning. In


particular, available P is low in the acid soils and, as elsewhere in Amazonia, probablylimiting to pasture growth. For local ranchers, the best source of nutrients is the standingforest, so every incentive exists to continue forest destruction for new pasture.

79

Powell, J.M. (1986): Manure for cropping: A case study from central Nigeria. ExperimentalAgriculture 22:15-24.

Keywords: maize; farming systems; fertilization; mixed farming; tropical savanna; WestAfrica; manure.

Abstract. The traditional management of cattle manure in a cropping system in the savannazone of central Nigeria is discussed in conjunction with the agronomic benefits and problemsof manure use. Nitrogen and phosphorus contents of the manure varied seasonally. On-farmtrials showed that maize grain yields were about 1 t ha-1 more and weed growth 90% greater inmanured than in non-manured areas. It is important to reduce the competition between cropsand weeds if grain crops are to obtain the full benefit of manure in such cropping systems.

80

McNaughton, S.J. and Stuart Chapin III, F. (1985): Effects of phosphorus nutrition anddefoliation on C4 graminoids from the Serengeti plains. Ecology 66:1617-1629.

Keywords: phosphorus; grassland; animal-plant interaction.

Abstract. Kyllingia nervosa (Cyperaceae) and Digitaria macroblephara (Poaceae), C4graminoids, were obtained from the Serengeti National Park of Tanzania. Kyllingia is mostabundant on high pH, high calcium, low phosphorus, carbonatic ash-derived soils, andDigitaria is more abundant on neutral, lower calcium, higher P soils. Both species come fromintensely grazed grasslands. Plant responses to different nutritional levels and defoliation weremeasured to evaluate potential limiting interactions between energy and nutrient flows ingrazing ecosystems. Plants were grown hydroponically at solution phosphorus concentrationsof 10 and 100 µmol/l and were either unclipped or clipped weekly to a height of 3 cm for 5wk. At that time, the kinetics of P uptake were measured with 32P, plants were harvested, anddry masses and the tissue concentrations of P and N were determined. Clipping and Pconcentration of the growth medium both had major effects upon yield of all plantcomponents. Total yield of Kyllingia was highest in unclipped plants at high levels of Psupply; yields under all other conditions were lower and undistinguishable from one another.In contrast, yield of Digitaria, which had been collected in areas with soils of higherphosphorus availability, was unaffected by defoliation but was almost 2½ times greater whenplants were grown at the higher P level. Root growth of Digitaria was stimulated bydefoliation when P was abundant. Maximum yield to grazers from Kyllingia under conditionsof this experiment would be achieved if grazers foraged only at the end of the period;maximum yield of Digitaria to grazers would be achieved if grazers defoliated plants atfrequent intervals. A variety of morphological changes associated with maintaining similarleaf areas whether clipped or unclipped were associated with Digitaria's ability to compensatefor simulated grazing. Yield to producers (the residual live biomass present at harvest) andyield to grazers were positively correlated, indicating that conditions promoting plant yieldcaused a proportional increase in yield to higher trophic levels. Further details about P and Nuptake and tissue concentrations in relation to the different treatments are reported.

References 73

81

Hutchinson, K.J. and King, K.L. (1982): Invertebrates and nutrient cycling. In: Lee, K.L.(ed.), Proceedings of the 3rd Australasian Conference on Grassland Invertebrate Ecology.Adelaide: S.A. Government Printer, p. 331-338.

Keywords: invertebrates; nutrient cycle; insects; Australia; pastures; soil biology; grassland;animal-plant interaction.

Abstract. The contribution of cycling to the phosphorus economy of a grazed fertilized pastureat Armidale was estimated to be 40 kg P ha-1 yr-1. The calculation was based on the differencebetween the total P in residues production and the yearly accumulation of organic P in the soil.23% of the residues P was from invertebrate corpses and excreta. However the amount andavailability of the mineral residues from invertebrates do not reflect the net functionalcontribution of these fauna to cycling. This depends largely on the ability to stimulatemicrobial activity. Progress in studies of the regulatory roles of invertebrates in cycling arereviewed. Mechanisms are grouped under the headings of particle reduction and abrasion,mixing, invertebrate dietary preferences, effects of microbial production, gut transactions anddirect effects of invertebrates on plant growth. Computer based studies on combinations andsequences of cycling mechanisms may be useful for defining the efficient nutrient strategieswhich may operate in grazing systems. Challenges in laboratory microcosm studies of cyclinginclude the choice of relevant invertebrate species, the inclusion of nutrient uptake by plants,the provision of a realistic spatial distribution of nutrients and the application of controlledenvironmental inputs to mimic the changes encountered in the field.

82

Lavelle, P. (1983): The soil fauna of tropical savannas. II. The earthworms. In: Bourliere, F.(ed.), Ecosystems of the world 13: Tropical savannas. Amsterdam-Oxford-New York:Elsevier Scientific Publishing Company, p. 485-504.

Keywords: soil fauna; tropical savanna; earthworms; pastures; species diversity; grassland.

Abstract. Tropical savannas can harbor a rich community of earthworms under favourableenvironmental conditions -- that is, when rainfall ranges from 1000 to 1500 mm, and is moreor less evenly spread over the whole year. In such cases, up to ten to twenty species can occurtogether, adequately sharing the food resources of the soil environment. Competition isavoided by food and space partitioning, and the variety of niches goes hand in hand withdifferent demographic structures and strategies. In man-made pastures located in formerlyforested areas, species diversity is lower and much depends on the adaptive potentialities ofthe former forest species to take advantage of these new environments, as well as on occasionfor pantropical species to invade these new habitats. In this perspective, the limited ability fordispersal of the earthworms is an obvious handicap. However, once established, thenewcomers can play a very important role, as the amount of humic material produced fromlitter and roots in moist tropical pastures can be important, and as the water regime of suchgrasslands is much more favourable for earthworms than that of a forest. In drier savannas, therole of earthworms becomes much less important when rainfall decreases and becomes moreand more seasonal and unpredictable. The long dry season of the Sahelian savannas makespermanent settlement by earthworms impossible.


83

Pfeffer, E. and Spiekers, H. (1989): Stickstoffbilanz in Milchviehbetrieben. DerTierzuechter 41:246-247.

Keywords: dairy cows; nitrogen; nutrient cycle; production level; farming systems; yields;pastures.

Abstract. Nitrogen balances in farming systems have become a matter of interest due topotential groundwater pollution from N-fertilizer use or organic residues of intensive animalproduction. The nitrogen balance in dairy farms depends mainly on the production level (milkyield per cow), use of feed concentrates and the area of pasture needed per cow. Modelcalculations for several production levels (milk and pasture yields) are given and the effectson the nitrogen balance of the system are discussed. (Abstract by bibliography authors)

84

García-Méndez, G., Maass, J.M., Matson, P.A. and Vitousek, P.M. (1991): Nitrogen trans-formations and nitrous oxide flux in a tropical deciduous forest in Mexico. Oecologia 88:362-366.

Keywords: nitrogen; Mexico; nitrogen cycle; nitrous oxide; tropical forest; pastures;atmosphere.

Abstract. Emissions of nitrous oxide and soil nitrogen pools and transformations weremeasured over an annual cycle in two forests and one pasture in tropical deciduous forest nearChamela, Mexico. Nitrous oxide flux was moderately high (0.5-2.5 ng cm-2 h-1) during thewet season and low (< 0.3 ng cm-2 h-1) during the dry season. Annual emissions of nitrogen asnitrous oxide were calculated to be 0.5-0.7 kg ha-1 yr-1, with no substantial difference betweenthe forest and pasture. Wetting of dry soil caused a large but short-lived pulse of N2O flux thataccounted for <2% of annual flux. Variation in soil water through the season was the primarycontrolling factor for pool sizes of ammonium and nitrate, nitrogen transformations, and N2Oflux.

85

Elliott, P.W., Knight, D. and Anderson, J.M. (1990): Denitrification in earthworm casts andsoil from pastures under different fertilizer and drainage regimes. Soil Biology andBiochemistry 22:601-605.

Keywords: denitrification; earthworms; pastures; fertilization; drainage; nitrous oxide;nitrogen.

Abstract. Laboratory incubations were carried out, with and without acetylene, of earthwormcasts and soil cores collected in permanent pastures with different fertilizer and drainageregimes. Nitrous oxide production (+C2H2) was consistently higher from casts than soilmaterial from all sites. In the undrained, unfertilized plot the mean rate of N2O productionfrom casts was nearly 5 times higher than from the soil. Moisture content was correlated withdenitrification for casts but not for soils although both materials were near to saturationthroughout the 8 week study. The proportion of endogenous N2O production (-C2H2) waslower in casts than soils indicating the more complete reduction of nitrogen oxides to N2

References 75

under aerobic conditions. Earthworm casts constitute important microsites for denitrificationand contribute to the spatial heterogeneity of these gaseous-N fluxes.

86

Plamondon, A.P., Ruiz, R.A., Morales, C.F. and González, M.C. (1991): Influence ofprotection forest on soil and water conservation (Oxapampa, Peru). Forest Ecology andManagement 38:227-238.

Keywords: Peru; hydrology; soil erosion; erosion control; tropical forest; pastures; waterquality; soil chemical properties; Brachiaria; sustainability; watershed; nitrogen; phosphorus.

Abstract. The demarcation of protection forest is a practice used in the mountainous areas ofthe Peruvian tropical forest to maintain ecological equilibrium. In order to evaluate some ofthe ecological effects of protection forest compared with other land uses, the effects ofdifferent land uses (dense natural forest, a mosaic of crop/pasture/forest, and pasture) on soilfertility and water quality were assessed on three basins within the Oxapampa municipalwatershed, near Cerro de Pasco. Samples were taken in dense forest, on a fresh clearcut, on aone-year-old regenerated site, on a site with regeneration cleared and burned, and crops andpastures at least 3 years old. Replacing the natural forest by pastures and crops reducedorganic matter, nitrogen, phosphorus, and potassium content of the soil. In addition, theincrease in exchangeable aluminium caused a substantial decrease in fertility three or moreyears after land clearance. Maximum suspended sediment concentrations reached 76, 226, and771 mg/litre respectively, for the three basins covered by forest, crop/pasture/forest, andpasture. From streamflow measurements, annual soil losses were, respectively 121, 345, and542 kg/ha. Water temperatures ranged from 13, 14, and 16 °C to a maximum of 14, 19, and 20°C, respectively. Minimum dissolved-oxygen concentrations of 7.7, 6.6, and 5.9 p.p.m. andpH of 7.0, 6.5, and 6.0 were measured. The results stress the importance of maintaining forestcover on steep land.

87

Takar, A.A., Dobrowolski, J.P. and Thurow, T.L. (1990): Influence of grazing, vegetationlife-form, and soil type on infiltration rates and interrill erosion on a Somalion rangeland.Journal of Range Management 43:486-490.

Keywords: erosion; infiltration; watershed; shrubs; hydrology; Somalia; grassland; grasses.

Abstract. Heavy communal grazing pressure and rapid phytomass decomposition reduce shrubinterspace cover in Somalia from 100% at the end of the growing season to 5% at the end ofthe dormant season. Intense monsoonal rains, characteristic of Somalia and other areas ofsubsaharan Africa, combined with sparse vegetative cover at the beginning of the rainyseason, may result on overland flow and excessive erosion, even where sand content of thesoil exceeds 90%. Little watershed research has been conducted in this region other than todocument that the problem is extreme. The objectives of this study were to assess the seasonalhydrologic responses as influenced by 2 soils (sand vs. clay), grazing intensity (exclusion vs.heavy communal grazing), and cover types (shrub understorey vs. interspace) in Somalia.Infiltration rate and interrill erosion on the sand site were significantly greater than on the claysite regardless of cover type or season. The clay site was dominated by annual forbs whichrapidly decomposed. The sand site had greater annual and perennial grass cover whichdecomposed slower than forbs, providing longer and perhaps better protection from raindrop


impact energy. Three growing seasons of livestock exclusion did not significantly increasesoil cover on shrub interspaces; consequently, infiltration rates and interrill erosion remainedsimilar to the communally grazed sites. Interspace cover left by livestock was instead removedby termites and other microorganisms. Restricted ability of livestock to graze beneath thornyshrubs and increased phytomass from shrub leaf-fall resulted in a greater accumulation ofcover and litter beneath shrubs, which aided infiltration on clay sites, regardless of season.

88

Lal, R. (1984): Soil erosion from tropical arable lands and its control. Advances in Agronomy37:183-248.

Keywords: soil erosion; erosion; tropics; deforestation; land-use changes; cover crops; mulch.

Abstract. The objective of this article is to evaluate, review, and assess the availableinformation on soil erosion in the tropics at its consequences, to identify knowledge gaps anddefine research and development priorities. In his study, Lal considers subjects, such asedaphic and climatic factors in relation to soil erosion, a comparison of soil erosion in tropicaland temperate climates, slope characteristics and scales of measurement, deforestation andchange in land use, soil erosion and crop productivity, soil loss tolerance and basic principlesof erosion control.

89

Banzhaf, J., Leihner, D.E., Buerkert, A. and Serafini, P.G. (1992): Soil tillage andwindbreak effects on millet and cowpea: I. Wind speed, evaporation, and wind erosion.Agronomy Journal 84:1056-1060.

Keywords: millet; erosion; deforestation; overgrazing; windbreaks; cowpea.

Abstract. Deforestation, overgrazing, and declining soil regeneration periods have resulted inincreased wind erosion problems in dry areas of West African Sahel, but little is known aboutthe bio-physical factors involved. This research was conducted to determine the effects ofridging and four different windbreak spacings on wind erosion, potential evaporation, and soilwater reserves. A field trial was conducted from 1985 to 1987 on 12 ha of a PsammenticPaleustalf in Southern Niger. Millet, Pennisetum glaucum (L.), and cowpea, Vignaunguiculata (L.) Walp., were seeded in strips on flat and ridged soil. Windbreaks of savannahvegetation were spaced at 6, 20, 40, and 90 m. The effects of ridging on wind speed,evaporation, and wind erosion were small and mostly non-significant. However, average windspeed at 0,3 m above ground in the center of cowpea and millet strips was significantlyreduced from 2.8 to 2.1 m/s as windbreak distances narrowed from 90 to 6 m. As aconsequence, potential evaporation declined by 15% and the amount of wind blown soilparticles by 50% in ridged and by 70% in flat treatments. Despite reduced potentialevaporation, average subsoil water reserves were 14 mm smaler in the 6- than in the 20-mwindbreak spacing indicating exessive water extraction by the windbreak vegetation. Thus,establishing windbreaks with natural savannah vegetation may require a careful considerationof agronomic benefits and costs to competing crops.

References 77

90

Nair, P.K.R. (1989): The role of trees in soil productivity and protection. In: Nair, P.K.R.(ed.), Agroforestry systems in the tropics. Dordrecht/NL: Kluwer Academic Publishers, p.567-589.

Keywords: trees; agroforestry; nitrogen; legumes; farming systems; erosion control; legumetrees; soil chemical properties; soil physical properties.

Abstract. Various aspects are covered: (1) suggested mechanisms of soil improvements inagroforestry (evidence from existing land-use systems, and the effect of trees on soils,including a table summarizing the potential benefits of trees to soils); (2) nitrogen fixing trees(including a table 'perennial legumes commonly used in Asian farming systems', which listsmainly nitrogen fixing trees); (3) nutrient cycling in agroforestry systems; (4) trees and soilconservation (the effects of trees on erosion factors, observed erosion rates under agroforestrypractices, and examples of the use of agroforestry in erosion control); and (5) trees aswindbreaks and shelterbelts (descriptions, species, benefits and examples).

91

Torssell, B.W.R. (1973): Patterns and processes in the Townsville Stylo-annual grass pastureecosystem. Journal of Applied Ecology 10:463-478.

Keywords: degradation; grass-legume pastures; erosion; Australia; weeds.

Abstract. Ecological relationships between Townsville stylo (Stylosanthes humilis H.B.K.)and annual grass weeds were examined in a pasture on cleared Tippera clay loam in northernAustralia. Changes in vegetation pattern over a 5-year period were found to be related to: (1)water run-off and infiltration modified by soil characteristics, plant cover and low amplituderelief; (2) surface transport of seed, soil and plant nutrients; (3) the effects of topsoil moistureon germination, seed mortality and seedling establishment; (4) the effects of soil water, soilfertility and grazing on competition between species. The stability of the vegetation patternwas expressed by a pasture stability index (PS) and by a real stability index for eachcomponent (RCS). Apparent component stability (ACS), based on net changes in componentoccupancy, was defined as an index to describe persistence of animal-carrying capacity. Inmost years pasture stability (PS) was maintained. A balance developed in the speciesdistribution in which the grasses were characteristic of the depressions in the pasture and thelegume characteristic of the slopes (slope gradient 1:400). In one year, however, followingintensive grazing and intense rainfall, water runoff and the consequent transport of seed wasso great that the pasture stability (PS) was substantially decreased. It has been possible toexpress the relations between the components of the pasture ecosystem diagramatically. Thediagram is thought to reflect those principles generally applicable to annual legume-grasspastures in dry monsoonal environments and to give guide lines for research in the future.Examination of the factors contributing to pasture instability appears to be of high priority.

92

Leach, G.J., Rees, M.C. and Charles-Edwards, D.A. (1986): Relations between summercrops and ground cover legumes in a subtropical environment. 1. Effects of a Vigna trilobataground cover on growth and yield of sorghum and sunflower. Field Crops Research 15:17-37.


Keywords: ground cover; legumes; Vigna trilobata; yields; Sorghum bicolor; Helianthusannuus; annual field crops; subtropics; erosion control; Australia; seeds; erosion.

Abstract. An annual form of Vigna trilobata (L.) Verdc., a semi-domesticated herbaceouslegume, was used to provide additional ground cover under rainfed crops in a subtropicalenvironment. This study reports effects of V. trilobata on growth and yield of sorghum(Sorghum bicolor (L.) Moench) and sunflower (Helianthus annuus L.). Crops were sown on avertisol in south-east Queensland in October and January at densities of 10 and 5 plants m-2

for sorghum and 5 and 2.5 plants m-2 for sunflower, and with or without ground cover legume.Crop rows were 0.8 m apart. V. trilobata seed was broadcast at 150 seeds m-2 when the cropswere sown. While a full profile of soil water at sowing, and 330 to 424 mm rainfall duringcrop growth, led to vigorous growth of both crops and ground cover, crops from both sowingsexperienced water stress from about anthesis to the middle of grain fill. At the higher cropdensity, yields of sorghum grain were 453 and 355 g m-2 and yields of sunflower seed were161 and 227 g m-2 after sowing in October and January, respectively. Yields were decreased to87%, 70%, 76% and 90% respectively in the presence of up to 330 g m-2 of dry matter of V.trilobata. Sorghum yields were marginally lower at the lower density and decreased relativelymore in the presence of ground cover. Neither the yield of sunflower seed, nor the effect ofground cover on it, was affected by density. Competition from ground cover decreasedradiation interception by crops through decreasing leaf area index. It did not appear to affectthe efficiency of conversion of intercepted radiation to dry matter. Tiller number in sorghumwas decreased by ground cover, except in the low density stand sown in October. Effects ofground cover on the contribution of tiller heads to yield were more severe, leading to a halvingof their contribution at the lower density. Lower grain yields in the presence of ground coverwere due to lower numbers of seeds m-2 in both crops. Seed size was also smaller insunflower, but the percentage of oil was not affected. We conclude that under well-wateredconditions in south-east Queensland the decreases in yields of summer crops in competitionwith V. trilobata are likely to be outweighed by the anticipated long-term benefit from usingground cover to decrease soil erosion. The need for information on the processes andconsequences of competition under dryer conditions is emphasized, so that we can evaluatethe broader potential for ground cover legumes in the subhumid tropics.

93

Costin, A.B. (1980): Runoff and soil and nutrient losses from an improved pasture atGinninderra, Southern Tablelands, New South Wales. Australian Journal of AgriculturalResearch 31:533-546.

Keywords: pastures; infiltration; sheep; nitrogen; phosphorus; fertilizers; legumes; groundcover; livestock; improved pastures; soil erosion; Australia.

Abstract. Plot and catchment measurements of runoff and of soil and nutrient losses werecarried out on a moderately to heavily grazed (12-30 sheep/ha) phalaris-subterranean cloverpasture at Ginninderra. The effects of an intense summer storm were examined by applyingartificial rains of 20 mm/15 min on 5.6 m2 runoff plots in 1964. The pasture topsoils had highinfiltration capacities (50-75 mm/h), and when dry could absorb more than 40 mm of water.Surface runoff and soil loss were inversely related to cover (as pasture, detached litter, andsheep dung). Cover values less than about 70% were associated with some large increases inrunoff and soil loss, whereas at higher cover values there was relatively little reduction inrunoff and soil loss. Most soil losses were small (<5 g/ m2) when runoffs were less than about15%, but increased rapidly with increasing runoff. Acceptable conditions of ground cover

References 79

were mostly maintained on the improved pasture but their potential for soil and nutrient losseswas greater than on native pasture. Pasture renovation substantially reduced surface runoff.The effects of natural rains on runoff and soil and nutrient losses were measured from 1966 to1971 on a 88 ha experimental catchment. The amount of runoff varied with the amount andseason of rainfall, from less than 1 mm (0.2% of rainfall) in a dry year to 51 mm (7%) in a wetyear, with an average of 29 mm (4%) per year. Most runoffs in autumn ad summer wererelatively small, reflecting the high infiltration capacity of the surface soil when topsoilmoisture storage was available. In spring and winter, when the topsoil was mostly wet, runoffswere greater, reflecting the much lower infiltration capacities (c. 5 mm/h) of the subsoil. Soillosses were related to the runoffs. They ranged from 4 kg to 376 kg/ha/year, with an averageof 179 kg. Most of the soil was in fine suspension, little as bed load or coarse floating debris.Losses of nitrogen, phosphorus, potassium and sulfur were at average rates of 0.62, 0.12, 1.93and 0.06 kg/ha/year. The present rate of soil loss is less than the estimated past rate of topsoildevelopment, and the rates of loss of nitrogen, phosphorus and sulfur are less than the inputsfrom fertilizers and legumes. With management to retain adequate ground cover, theGinninderra pasture effectively controls runoff and soil and nutrient losses, and could be usedin similar environments as a standard for soil and water conservation, as well as livestockproduction.

94

Nitis, I.M., Lana, K., Suarna, M., Sukanten, W. and Putra, S. (1990): Three strata foragesystem for smallholder in dryland farming area. Indonesian Agricultural Research andDevelopment Journal 12:23-28.

Keywords: grasses; legumes; Leucaena leucocephala; trees; annual field crops; cattle;fuelwood; soil erosion; agroforestry; Gliricidia sepium; Ficus poacellii; Lanneacoromandelica; Hibiscus tiliaceus; Indonesia; economics; silvopastoral systems; erosioncontrol; legume trees; shrubs; yields; natural pastures; pastures.

Abstract. The concept and development of a 3-strata forage system (grasses and groundlegumes), shrubs (Gliricidia sepium, Leucaena leucocephala) and fodder trees (Ficuspoacellii, Lannea coromandelica, Hibiscus tiliaceus) designed to provide year-round animalfeed is described. Food, forage and fodder crop yields, liveweight gains of cattle, fuelwoodproduction, changes in soil fertility, and farm labour and income, are summarized from 5.5years (1984-89) of observations. Cattle production was higher, and soil erosion less, with the3-strata system than with the traditional system of using natural pastures for tethered grazing.Constraints and possible improvements in the 3-strata system are outlined. (Abstract bybibliography authors)

95

Prinz, D. and Rauch, F. (1987): The Bamenda model. Development of a sustainable land-usesystem in the highlands of West Cameroon. Agroforestry Systems 5:463-474.

Keywords: sustainability; farming systems; erosion control; trees; agroforestry; Eucalyptus;manure; shrubs; fallow; legumes; grasses; Cameroon; mixed farming; energy balance;cassava; beans; pastures; fruit trees; oil palms; annual field crops.

Abstract. Since 1980 in the western highlands of Cameroon, on the Bamenda plateau, the so-called Bamenda model has been developed. This model is an attempt to build up, essentially


with local resources, an ecologically stable and economically attractive land use system. Keyelements are the introduction of draught oxen, the implementation of integrated plant nutritionsystems, erosion control with contour bunds, the avoidance of soil-turning ploughing, and theintegration of trees and shrubs into the system. The model uses the autochthonous experiencesof the population, leads to the integration of the male population into food production, andalleviates the work load through emphasis on animal traction. A typical model farmcomprises: (1) an agroforestry sector (planted with: oil palms, Elaeis guineensis; raffia palms,Raphia hookeri; Albizia and Eucalyptus species; various fruit trees; coffee; and other cropssuch as plantain, papaya, pineapple, bitterleaf and taro); (2) homestead and cattleshed withroofed-over manure deposit; (3) house garden or women's plot; (4) leguminous hedges; (5)planted fallow plot; (6) contour bunds (sometimes planted with plantain, coffee, cassava orperennial legumes); (7) field strips between the bunds under mixed cropping (e.g. beans, taro);(8) improved pasture (planted with high-yielding grasses and grazing legumes). Otherelements include animal husbandry (pigs, goats, poultry, rabbits), the use of traditional crops,and the supply of fuelwood and construction timber. Energy balance and labour aspects of thesystem are analysed.

96

Benge, M.D. (1987): Multipurpose uses of contour hedgerows in highland regions. WorldAnimal Review 64:31-39.

Keywords: reforestation; agroforestry; dry-season feed; erosion control; forage trees; legumetrees; legumes; sustainability; tropical highlands.

Abstract. The important element of contour hedgerow systems, presented in this article, is theuse of multipurpose woody perennials on steep areas for the production of forage forlivestock, and of large amounts of vegetatively propagated planting stock for large-scalereforestation as well as increased crop yields, added soil organic matter, reduced erosion andwater runoff, increased ground-water infiltration, and fuelwood.

97

Gardener, C.J., McIvor, J.G. and Williams, J. (1990): Dry tropical rangelands: solving oneproblem and creating another. Proceedings of the Ecological Society of Australia 16:279-286.

Keywords: rangeland; livestock; degradation; stocking rate; improved pastures; feedsupplements; overgrazing; shrubs; soil erosion.

Abstract. The open woodlands of northern Queensland have been grazed by domesticatedlivestock for approximately 120 years. Botanic shifts occurred, but there was relatively littledegradation during the first 100 years. The main limitation to cattle production was poorquality herbage. Stocking rates were low to enable maximum selection of the most nutritiousplants. Mortalities in the British breeds were high during droughts and subsequent herd buildup was limited by poor breeding performance. To improve cattle nutrition, graziers adoptedfeed supplements and better-adapted zebu cattle. This resulted in greatly improved survivaland growth rates, with an accompanying increase in herbage consumption and grazingpressure. Some pastures, particularly in the "better" areas (e.g., Burdekin catchment) are nowsuffering from severe overgrazing with loss of herbaceous cover, shrub invasion and soilerosion. Only a reduction in grazing pressure can prevent rapid expansion of this problem.Pasture improvement can only help solve the problem if stocking rates are not again increased

References 81

to recoup the investment. In the Burdekin catchment, silt and suspended colloids in the dam,irrigation aquifers and water filtration plants will lead to pressures to moderate land use.

98

Ellison, L. (1960): Influence of grazing on plant succession of rangelands. The BotanicalReview 26:1-78.

Keywords: animal-plant interaction; overgrazing; degradation; ecological impacts; fireecology; soil erosion; mulch; microclimate; USA; plant succession; rangeland.

Abstract. This review is concerned with secondary succession as a result of humanmanagement of the range resource, whilst primary succession refers to natural changes ofplant cover through action and interaction of organisms and the environment. Successionaltrends by major plant types of the United States are examined, beginning with the true prairieof the Great Plains and moving westward. Rather than dwelling on the generally knowndestructiveness of overgrazing, the effects of light or moderate grazing shall be evaluated, inorder to build a picture of the ecological influence of grazing on plant composition. Inaddition, the effects of herbage removal on the individual plant and on the environment areexamined, with the objective of learning to what extent grazing can be considered aconstructive ecological force. (Abstract by bibliography authors)

99

Stephenson, G.R. and Veigel, A. (1987): Recovery of compacted soil on pastures used forwinter cattle feeding. Journal of Range Management 40:46-48.

Keywords: pastures; cattle; soil compaction; soil physical properties.

Abstract. Soil bulk density measurements were taken from pastures used for winter feeding todetermine the effects of different stocking rates on soil compaction and recovery. Sampleswere taken from paired ungrazed (control) pastures, normally grazed pastures (10 head perha), and pastures grazed 4 times normal. Results show that significant differences occur in soilbulk density with increased stocking rates, and that 2 growing seasons with protection fromgrazing and trampling are insufficient time for complete recovery.

100

Pinzón, A. and Amézquita, E. (1991): Compactación de suelos por el pisoteo de animales enpastoreo en el piedemonte amazónico de Colombia. Pasturas Tropicales 13(2):21-26.

Keywords: Colombia; Brachiaria decumbens; pastures; cattle; soil physical properties; soilcompaction; tropical forest; South America.

Abstract. The effect of grazing animals on some soil physical properties was measured at theCentro de Investigaciones ICA-Macagual (piedmont of Caquetá), at 1°37' N and 75°36' W,within the tropical rain forest ecosystem. Measurements were made on geomorphologicalpositions of slightly hilly areas (clay Typic Hapludult), low terrace (clay typic Dystropept),and valley plain (clay-loam-silt Fluvaquentic Dystropept), with Homolepis aturensis andBrachiaria decumbens pastures grazed for 10 years. Measurements were also made for nativeforest. Animal trampling modifies soil physical characteristics. In clay soils, compaction was


greater, and in some cases soil loss occurred in the first 15 cm. The apparent density increasedas soil depth increased, independently from the geomorphological position, which decreasesinternal movement of water in the soil. These changes were more drastic in H. aturensis. Tothe contrary, B. decumbens improved soil filtration because of a better structure anddistribution of macroporosity. The results suggest that in the piedmont of Caquetá, Colombia,cattle raising should be done with improved species that favour the existing soil structure.

101

Alegre, J.C. and Lara, P.D. (1991): Efecto de los animales en pastoreo sobre las propiedadesfísicas de suelos de la región tropical húmeda de Perú. Pasturas Tropicales 13(1):18-23.

Keywords: tropical forest; Peru; pastures; cattle; soil physical properties; soil compaction;South America.

Abstract. On a sandy loam Ultisol, since 1980 at the San Ramón Experiment Station (humidtropical forest), Loreto, Peru, pasture productivity has been evaluated in: Centrosemapubescens CIAT 438, Brachiaria humidicola-Desmodium ovalifolium, B. decumbens-D.ovalifolium, Andropogon gayanus-Stylosanthes guianensis, and A. gayanus-C. macrocarpum.Some measurements of these pastures were taken after five years to determine the effect ofgrazing animals on the physical properties of the soil. It was found that (1) The infiltration ratewas greater in the crown area of the soil under A. gayanus plants (> 16.5 cm/hour) than amongthe grass plants where animals normally walk. (2) Conical resistance of the soil underassociations was greater than that of soil under forest, but less than that under overgrazednative pasture. (3) The apparent density in the first 10 cm of the soil increased 17.5%, onaverage, in the soil under associated pastures, and 29.1% under native pasture in relation tothe secondary forest. The results show that animals grazing on humid tropical forest soilsreduce the infiltration rate and increase the apparent density.

102

Wilcox, B.P. and Wood, M.K. (1988): Hydrologic impacts of sheep grazing on steep slopesin semiarid rangelands. Journal of Range Management 41:303-306.

Keywords: sheep; infiltration; hydrology; soil physical properties; semiarid zones.

Abstract. Infiltration, sediment concentration of runoff, and sediment production from lightlygrazed and ungrazed semiarid slopes were compared using a hand-portable rainfall simulator.The study slope was located in the Guadelupe Mountains of southeastern New Mexico.Average slope steepness was 50%. The objective of this study was to determine the impacts oflight grazing by sheep (10 ha/AU) on steep slope infiltrability and sediment production.Infiltrability on the grazed slopes was 12-17% lower than on ungrazed slopes. These resultsare comparable to what has been reported from moderate slope gradients. Sedimentconcentration of runoff from the lightly grazed slopes was significantly higher than from theungrazed slopes only at the end of the dry run (45 min). Sediment production was significantlygreater from the grazed slopes for the dry run, but not the wet run. Percentage difference ofsediment production between the grazed and ungrazed slopes was well within the rangepublished for moderate slope conditions. These data give no indication that steep slopes (30-70%) in semiarid regions are any more hydrologically sensitive to light grazing than aremoderate slopes (<10%).

References 83

103

Warren, S.D., Blackburn, W.H. and Taylor Jr., C.A. (1986): Soil hydrologic response tonumber of pastures and stocking density under intensive rotation grazing. Journal of RangeManagement 39:500-504.

Keywords: pastures; rotational grazing; stocking rate; hydrology; soil physical properties;livestock; infiltration.

Abstract. Infiltration rate and sediment production were measured for 2 years on 3 pasturesfrom an intensive rotational grazing system. The pastures were 32, 24 and 16 ha in size.Stocking rate was held constant but stocking density at any given point in time varied due topasture size. Stocking densities were 0.68; 0.51; and 0.32 ha/AU, respectively. Within therespective treatments, midgrass interspaces exhibited significantly higher infiltration rates andlower sediment production than shortgrass interspaces. Overall, the pasture grazed at thehighest stocking density produced the lowest infiltration rates and the greatest sediment loss.However there was no consistent trend in hydrologic responses over time and the differencesappeared to be the result of stocking density. Regardless of whether the pasture grazed at thehighest stocking density was in similar or poorer hydrologic condition in terms of treatmentresponse, the data do not support the hypothesized beneficial hydrologic advantages ofincreased stocking density via manipulation of pasture size and numbers. Rest, rather thanintensive livestock activity, appears to be the key to soil hydrologic stability. The potential foraltering the length of the rest period is greatest where the number of pastures is small.Therefore, very little benefit in terms of soil hydrologic condition should be expected fromlarge increases in the number of pastures within rotational grazing systems.

104

Akobundu, I.O. and Okigbo, B.N. (1984): Preliminary evaluation of ground covers for useas live mulch in maize production. Field Crops Research 8:177-186.

Keywords: legumes; grasses; live mulch; maize; weed control; earthworms; erosion control.

Abstract. Several ground covers were assessed over a 2-year period to determine their effectson weed competition and maize yield. Maize was planted directly into established groundcovers of Axonopus compressus (Sw.) Beauv., Desmodium triflorum (L.) DC, and Indigoferaspicata Forsk. Planting rows in Arachis repens Handro plots were marked by manuallypulling of stem segments of the legume cover. While Paspalum notatum Fluegge cover wasfirst killed with glyphosate (3.6 kg/ha) before planting maize, several legume managementmethods that included slashing and spraying with either paraquat or a hormone were evaluatedfor use in Centrosema pubescens Benth. and Psophocarpus palustris Desv. Weed infestationwas heaviest in Axonopus compressus, Desmodium triflorum, Indigofera spicata and no-tillage; moderate in the Arachis repens and maize stover; and very low in Centrosemapubescens and Psophocarpus palustris. Maize yield was highest in the maize stover andpoorest in the Indigofera spicata. Good maize yield was obtained in the live mulch in whichweed competition was minimized by the legume cover. This technique promises to eliminateor significantly reduce weeding since over 40% of farmers' time in the humid tropics isdevoted to weeding.


105

Kang, B.T., Reynolds, L. and Atta-Krah, A.N. (1990): Alley Farming. Advances inAgronomy 43:315-359.

Keywords: deforestation; degradation; tropics; Africa; trees; legumes; mulch; green manure;livestock; erosion control; Asia; alley cropping.

Abstract. Rising demand for food and feed has resulted in increased deforestation and landdegradation in many parts of the tropics. In sub-Saharan Africa food production relies mainlyon area expansion and the use of traditional farming methods that depend on inherent soilfertility. In the 1980s research attention has been focused on the development of low inputtechnologies for sustainable food production for smallholder farmers. One such technology isalley farming. Alley farming involves the cultivation of food crops between hedgerows ofmultipurpose trees. Use of woody legumes provides N-rich mulch and green manure tomaintain soil fertility and enhance crop production, and protein-rich fodder for livestock. Onsloping land, hedgerows planted along the contours greatly reduce soil erosion. Within theforest zone, and particularly in the forest-savanna transition areas of Africa with nonacid soils,on-station and on-farm trials have shown that alley farming with Leucaena and Gliricidiaallows a higher level of production than the traditional system. Similar results have also beenobtained in comparable agro-ecological zones in Asia and the Pacific regions.

106

Vásquez, S.S. (1991): The establishment of forage legumes under field conditions in theColombian coffee zone. Dissertation Abstracts International 52:2361B-2362B.

Keywords: establishment; legumes; Centrosema macrocarpum; Pueraria phaseoloides;Desmodium ovalifolium; Leucaena leucocephala; grasses; Colombia; erosion; Centrosemapubescens; Arachis pintoi; Brachiaria decumbens; ground cover; live mulch; soil erosion.

Abstract. In 1988, 6 legumes (Centrosema macrocarpum CIAT 5065, C. pubescens CIAT438, Pueraria phaseoloides CIAT 9900, Arachis pintoi CIAT 17434, Desmodium ovalifoliumCIAT 350 and Leucaena leucocephala CIAT 17481) were assessed for their ability toestablish (cover the ground) and grow (produce DM) either alone or in combination with thegrass Brachiaria decumbens, using minimum soil disturbance, at 2 sites in Colombia (1708and 2500 mm precipitation). A. pintoi was the best legume in terms of soil cover and DMproduction. No inoculation response was found for most of the legumes except C.macrocarpum CIAT 5065 inoculated with Rhizobium strain CIAT 3101. The establishmenttime under these conditions was 3 months. Legume DM production and cover were affectedby continuous cutting close to the ground. The establishment of legumes other than A. pintoiwas slower and needed more weeding, increasing cost and the risk of soil erosion. D.ovalifolium and L. leucocephala could not be established by seed directly in the field becauseof their low competitive abilities against native grasses. Data from runoff plots set up in 1989showed that it was possible to establish grass-legume mixtures among the native grass(Paspalum spp.) without causing soil disturbance and increasing erosion. No variation in Ncontent of grass and legumes was found between blocks, but soil cover and DM productiondiffered between blocks located along and across the slope.

References 85

107

Leihner, D.E., Buerkert, A., Banzhaf, J. and Serafini, P.G. (1993): Soil tillage andwindbreak effects on millet and cowpea: II. Dry matter and grain yield. Agronomy Journal85:400-405.

Keywords: windbreaks; millet; cowpea; yields; West Africa; Africa; ground cover.

Abstract. In the West Africa Sahel, sand storms occurring early in the growing season mayseverely damage emerging crops. This study was conducted to determine the influence ofridges and windbreaks on growth, water use and grain yield of millet, Pennisetum glaucum(L.), and cowpea, Vigna unguiculata (L.) Walp. A field trial was carried out from 1985 to1987 on a Psammentic Paleustalf in southern Niger using 12 ha of land fallowed over theprevious 5 yr. Treatments for millet and cowpea were flat and ridged soil preparation andwindbreaks spaced at 6, 20, 40, and 90 m. Total annual rainfall was 558, 641, and 363 mm inthe 3 yr of the experiment; onset and distribution of the rains varied. Millet total dry matter(TDM) increased as total water use increased from 250 to 400 mm. Ridging did not changetotal dry matter or grain yield in millet but increased cowpea grain yield by 90 and 300 kg/hain 2 of the 3 yr. Protection by windbreaks spaced 6 and 20 m apart resulted in a 48 to 90%increase in early millet TDM and a 74 to 89% improvement of cowpea ground cover.However, these early effects were not sustained throughout the growing perod. Average TDMat maturity and grain yields were similar in all windbreak spacings for millet and cowpea.Although windbreaks may not increase yields of two important Sahelian crops, they may helpto stabilize longterm crop production by conserving the soil and providing additionalmarketable commodities if an appropriate selection is made of type of windbreak and speciesplanted.

108

Renard, C. and Vandenbeldt, R.J. (1990): Bordures d'Andropogon gayanus Kunth commemoyen de lutte contre l'érosion éolienne au Sahel. Agronomie tropicale (Paris) 45:227-231.

Keywords: erosion control; annual field crops; millet; Andropogon gayanus.

Abstract. In the Sahel zone, wind erosion is one of the major problems due to the sandy soiltexture and the incomplete vegetation cover. The problem is further aggravated by strongwinds occurring at the beginning of the rainy season. The sands transported during theseevents destroy or cover crop seedlings. In 1986, an investigation was started about thepotential of a perennial grass, Andropogon gayanus Kunth, to reduce wind erosion and protectmillet crops. 10 m large Andropogon-strips had no positive effect on grain yields of millet, butprotected well against the violent winds at the beginning of the growing season. These stripscaptured more than 2000 t/ha of sand within three years. The use of this pasture species fordemarcation of field boundaries is proposed.

109

Fedoseev, A.P., Gringof, I.G., Nurberdyev, M. and Reizvikh, O.N. (1982): Environmentaleffect of phytomeliorative plantings on pastures. (In Russian). Problemy Osvoeniya Pustyn6:27-33.


Keywords: pastures; deserts; Turkmenistan; trees; shrubs; microclimate; erosion control;moisture collection; marginal lands.

Abstract. Differences between the meteorological parameters of natural and artificial desertvegetation and landscapes were examined on the basis of field investigations in the desertzone of Turkmenistan. Artificial tree and shrub plantings reduce wind speed and daily rangesof soil and air temperature changes. They have a noticeable effect on the redistribution ofrainfall, particularly by interception and trunk runoff which can be 1-25% of totalprecipitation. The depth of wetting the soil under tree crowns increased on the windward sideand decreased on the leeward. These characteristics of the hydrometeorological regime underthe crowns of plantings have an effect on the formation of unique plant associations andforage productivity of pastures increases. (Abstract by bibliography authors)

110

Atta-Krah, A.N., Sumberg, J.E. and Reynolds, L. (1986): Leguminous fodder trees in thefarming system - an overview of research at the humid zone programme of ILCA insouthwestern Nigeria. In: Haque, I., Jutzi, S. and Neate, P.J.H. (eds.), Potentials of foragelegumes in farming systems of sub-Saharan Africa. Proceedings of a workshop held at ILCA,Addis Ababa, Ethiopia, 16-19 September 1985. Addis Ababa, Ethiopia: ILCA (InternationalLivestock Centre for Africa), p. 307-329.

Keywords: trees; Nigeria; forage trees; West Africa; legumes; Gliricidia sepium; adaptedgermplasm; Leucaena leucocephala; intercropping; legume trees; alley cropping; mulch;annual field crops; yields; animal production; sheep; farming systems.

Abstract. The potential of leguminous fodder trees in farming systems of humid West Africais considered in the light of research work carried out by the Humid Zone Programme of theInternational Livestock Centre for Africa (ILCA) at Ibadan, Nigeria. ILCA's agronomyresearch effort focuses on the leguminous species, Leucaena leucocephala and Gliricidiasepium. The paper reviews a variety of research trials ranging from the improvement ofgermplasm materials to the development of fodder production systems, and concludes with arecommendation for more research and development attention on the integration of foddertrees within existing farming systems.

111

Cameron, D.M., Gutteridge, R.C. and Rance, S.J. (1991): Sustaining multiple productionsystems. 1. Forest and fodder trees in multiple use systems in the tropics. Tropical Grasslands25:165-172.

Keywords: Australia; sustainability; silvopastoral systems; alley cropping; agroforestry;degradation.

Abstract. The benefits of introducing or maintaining a tree component in land use systems arebecoming attractive for land rehabilitation and sustainable production purposes. Increasingevidence supports the view that multiple production systems involving trees have somebeneficial economic and environmental consequences in many land use programs throughoutAustralia. Coordinated research to support these approaches and to demonstrate theirimplementation and potential is now needed to complement fragmentary research throughoutthe country. Government policy towards forestry and agroforestry requires redefinition to

References 87

provide production incentives to increase the impact of the environmental thrust. Trees haveoften been included in farm planning for amenity purposes, particularly around farm housesand buildings but less frequently to provide shade and shelter for animals, crops and pasturesor to reduce the harmful effects of rising watertables, especially those containing salt.Advantages and disadvantages of including trees in multiple land use systems are listed andtheir role and potential discussed. There is considerable potential to expand private timberproduction in agroforestry systems to offset the very large import bill for timber and forestproducts.

112

Walker, B.H. (1974): Ecological considerations in the management of semi-arid ecosystemsin south-central Africa. Proceedings, 1st International Congress of Ecology. Wageningen:Centre for Agricultural Publishing and Documentation, p. 124-129.

Keywords: ecosystems; Africa; infiltration; grasses; species diversity; trees; grazing; cattle.

Abstract. There are four significant ecological characteristics of semi-arid ecosystems insouth-central Africa which have an important bearing on their management. i) They have alow erratic rainfall which is closely correlated with primary production. ii) The rate of waterinfiltration is critical and is determined by the percentage litter cover and herbaceous basalcover. On sandy loam soils it is nine times faster through soil under litter than through a baresoil surface. iii) Species composition varies markedly according to the proportions ofperennial and annual grasses, the palatability of the perennials, and species diversity. Annualgrasses increase interseasonal variation in production. Seasonal production is positivelycorrelated with an increase in species diversity. iv) There is evidence that clearing woodyvegetation can lead to increases of up to 400% in grass growth, but this must be balancedagainst a number of benefits derived from the presence of trees. Five management principlesare discussed. i) The ration of grazing to browsing should approximate the ratio of grass toavailable browse. ii) Area selective grazing should be overcome by five suggested means. iii)Cattle should be managed using multi-paddock, short duration grazing systems. iv) The use offire, especially on lithosols, should be avoided. v) In National Parks and game reserves,animal numbers and fires should be controlled, but the introduction of artificial water suppliesinto characteristically dry areas should be avoided.

113

Lenné, J.M., Turner, J.W. and Cameron, D.F. (1980): Resistance to diseases and pests oftropical pasture plants. Tropical Grasslands 14:146-152.

Keywords: diseases; pests; pest resistance; pastures; pest control; genetics; breeding; adaptedgermplasm.

Abstract. In recent years, increasing numbers of pathogens and pests have been reported frommajor centres of tropical pasture research. Damage is often severe and controls are needed.Diseases and pests may be controlled chemically, biologically, culturally and genetically. Inpasture plants, genetical resistance is the most practical and economical control method and,as a component of integrated pest management, has considerable potential in controlling pests.Tropical pasture plants have been artifically selected for only a short time. Vast sources ofgenetic variation exist in their centres of diversity. This natural variation should be utilized inselecting for resistance before initiating long term breeding programmes. Evaluation of


resistance to diseases and pests of tropical pasture plants requires understanding of the plant,the pathogen or pest, the environment and their interactions. Primary germplasm evaluationfor resistance in plant centres of diversity is strongly recommended and high priority shouldbe given to understanding resistance mechanisms. The importance of multidisciplinecollaborative research on resistance to diseases and pests of tropical pasture plants is stressed.

114

Ceccarelli, S., Valkoun, J., Erskine, W., Weigand, S., Miller, R. and van Leur, J.A.G.(1992): Plant genetic resources and plant improvement as tools to develop sustainableagriculture. Experimental Agriculture 28:89-98.

Keywords: genetics; Asia; Africa; wheat; pastures; genetic erosion; livestock; insects; insectpests; pests; diseases; yields; ecosystems; biological control; germplasm; sustainability.

Abstract. This paper addresses the current and future contributions of plant genetic resourcesand plant improvement to sustainable agriculture with reference to the activities of theInternational Center for Agricultural Research in the Dry Areas (ICARDA) in association withnational programmes in West Asia and North Africa. These regions constitute the primarycentres of diversity of crops (wheat, barley, chickpea, lentil) and a number of pasture andforage species. Genetic erosion is being curtailed by germplasm collection and preservation.Selection for low-input cultivars of barley is conducted under low input conditions, and newcultivars of lentil and barley are often intentionally heterogeneous to stabilize theirperformance in dry rainfed areas. The importance of genetic differences in the cultivars onsubsequent crops in the rotation and on straw quality for livestock is under study. Insect pestsand diseases contribute to yield instability. Because of the potential adverse impact ofpesticides on the fragile ecosystems of the region, integrated control strategies based onagronomic management, host plant resistance, biological control agents and strategic use ofselective insecticides are being developed.

115

Atu, U.G. and Ogbuji, R.O. (1984): Effect of cover plants in fallow lands on root-knotnematode population. Beiträge zur Tropischen Landwirtschaft und Veterinärmedizin 22:275-280.

Keywords: Nigeria; improved fallow; cover crops; pest control; pest resistance; nematodes;Meloidogyne incognita; legumes.

Abstract. In southern Nigeria, cover plants were evaluated for their resistance to root-knotnematode, Meloidogyne incognita race 2. In glasshouse and field experiments, Crotalariaretusa, Arachis hypogaea, Stylosanthes gracilis, Tagetes patula, and T. erecta were found tobe highly resistant; Centrosema sp., Panicum maximum, Eupatorium odoratum and Aspilialatifolia exhibited a medium degree of resistance, and Calopogonium sp., Cajanus cajan,Vigna unguiculata, and Cynodon dactylon were susceptible. Planting cover crops thatsuppress root-knot nematodes in fallow lands could become a way of field pest managementpractice.

References 89

116

Rodriguez-Kabana, R., King, P.S., Robertson, D.G., Weaver, C.F. and Carden, E.L.(1988): New crops with potential for management of soybean nematodes. Nematropica 18:45-52.

Keywords: soybeans; nematodes; Aeschynomene americana; Meloidogyne arenaria;Heterodera glycines; Alysicarpus vaginalis; legumes; sorghum; green manure; pest control;crop rotation.

Abstract: American jointvetch (Aeschynomene americana), 'Florida 101' hairy indigo(Indigifera hirsuta), and 'Iron' cowpeas (Vigna unguiculata) were more effective in reducingroot-knot nematodes (Meloidogyne arenaria and M. incognita) and soybean cyst nematode(Heterodera glycines) race 4 in a greenhouse experiment than were alyceclover (Alysicarpusvaginalis), Kobe lespedeza (Lespedeza striata), Korean lespedeza (Lespedeza stipulacea) andDavis' soybean (Glycine max). The effects of American jointvetch and hairy indigo on soilpopulations of the three nematode species were also studied in a field in Baldwyn County,Alabama. Soils from plots with the two legumes was essentially free of juveniles of root-knotand cyst nematodes throughout the growing season. Juvenile populations in these plots wereas low as those in plots planted to 'Pioneer 8222' sorghum (Sorghum bicolor). Plots with'Kirby' soybean had large juvenile populations (150 juveniles/100 cm3 of soil) of root-knotnematodes 1 month before harvest; numbers of H. glycines juveniles averaged 85/100 cm3 ofsoil. Results suggest that American jointvetch and hairy indigo may be forage or green manurecrops with potential for the management of soybean nematodes in Alabama.

117

Domínguez-Valenzuela, J.A., Marban-Mendoza, N. and de la Cruz, R. (1990):Leguminous crops associated with tomato var. "Dina guayabo" and their effect onMeloidogyne arabicida Lopez and Salazar. Turrialba 40:217-221.

Keywords: Pueraria phaseoloides; Arachis pintoi; Centrosema pubescens; Desmodiumovalifolium; Centrosema acutifolium; legumes; nematodes; Meloidogyne arabicida; tomatoes;intercropping; Centrosema macrocarpum; pest control.

Abstract. When Pueraria phaseoloides, Arachis pintoi and Centrosema pubescens were co-cultivated with tomato var. Dina guayabo in greenhouse pot tests, a significant reduction ingalling caused by M. arabicida was observed on tomato. The leguminous plants Desmodiumovalifolium, Centrosema acutifolium, C. pubescens and C. macrocarpum generally gave alesser degree of root galling under the same conditions. All legumes tested caused a slightreduction in the vegetative growth of tomato plants. However, growth was significantlyreduced when compared to plants infested only with M. arabicida (control treatment).Consequently, it is thought that reduced plant size was primarily due to competition betweenlegumes and tomato plants. The plants associated with A. pintoi, which reduced root gallingby almost 50%, did not gain in vegetative growth. Only C. pubescens and C. acutifoliumdeveloped a few small-sized (1.2 mm) galls (1%) and did not support M. arabicida females.


118

Rodriguez-Kabana, R., Weaver, D.B., Robertson, D.G., Young, R.W. and Carden, E.L.(1990): Rotations of soybean with two tropical legumes for the management of nematodeproblems. Nematropica 20:101-110.

Keywords: legumes; nematodes; yields; Meloidogyne arenaria; soybeans; Heteroderaglycines; Aeschynomene americana; Indigofera hirsuta; annual field crops; pest control.

Abstract. The effects of two tropical legumes, American jointvetch (Aeschynomeneamericana) and hairy indigo (Indigofera hirsuta), in rotations with soybean on populations ofroot-knot (Meloidogyne arenaria) and cyst (Heterodera glycines) nematodes and on soyabeanyields were studied in 2-year field experiment. End-of-season juvenile soil populations of M.arenaria and H. glycines were reduced by 95-100% where either of the tropical legumes wasgrown. Yields of 7 soybean cultivars (Braxton, Centennial, Gordon, Kirby, LeFlore, Ransom,Stonewall) increased significantly in plots planted with jointvetch or indigo the previous year.The magnitude of the yield increment depended on the soybean cultivar; the average increasesin yields for all cultivars were 46% and 55% following jointvetch and indigo, respectively. At-plant application of aldicarb (17 g a.i./100 m of row in a 20-cm-wide band) was most effectivein increasing yields of soybean grown in monoculture but was generally ineffective in soybeangrown in rotation. The suppressive effect of the tropical legumes on end-of-season juvenilesoil populations of M. arenaria and of H. glycines was short-lived; end-of-season juvenilepopulations in plots with soybean planted with either jointvetch or hairy indigo the previousyear were equal or greater than the populations found in plots with continuous soybean.

119

Reddy, K.C., Soffes, A.R., Prine, G.M. and Dunn, R.A. (1986): Tropical legumes for greenmanure. II. Nematode populations and their effects on succeeding crop yields. AgronomyJournal 78:5-10.

Keywords: legumes; green manure; nematodes; pest control.

Abstract. The effects of tropical legumes, grown as summer green manure crops, onpopulations of 4 plant-parasitic nematodes were compared with fallow and 'Cracker Jack'marigold (Tagetes erecta) in fumigated (with 1,2-dibromethane) and nonfumigated plots in1979, 1980 and 1981 on an Arrendono fine sand (loamy, siliceous, hyperthermic, GrossarenicPaleudult). Long-term effects of summer legume green-manuring on nematode populationsand yield of succeeding crops was determined using several cereals and legumes grown in thesucceeding autumn, winter and spring seasons. One cultivar, 'Norman', and one line, 'F181d',of pigeonpea (Cajanus cajan), showy crotalaria (Crotalaria spectabilis), hairy indigo(Indigofera hirsuta), jointvetch (Aeschynomene americana), velvet bean (Mucunadeeringiana) and marigold reduced soil populations of Meloidogyne incognita in each yearplanted; 'PI 305070' mungbean (Vigna radiata) did not. Fumigation, fallowing and rotationwith jointvetch, hairy indigo and crotalaria reduced Belonolaimus longicaudatus populations.Rotation with hairy indigo or marigold consistently reduced Pratylenchus brachyurus in allthe succeeding crops. Fumigation generally reduced Criconemoides spp. populations. M.incognita and the incorporated green manure had the greatest influence on snap bean(Phaseolus vulgaris) cv. 'Blue Lake Bunch' dry matter yield.

References 91

120

Wildermuth, G.B. and McNamara, R.B. (1991): Effect of cropping history on soilpopulations of Bipolaris sorokiniana and common root rot of wheat. Australian Journal ofAgricultural Research 42:779-790.

Keywords: legumes; grasses; crop rotation; wheat; Cochliobolus sativus; fungal diseases;Australia; annual field crops; fallow; disease control.

Abstract. Six winter and 4 summer crops, 2 pasture legumes and 2 pasture grasses, weregrown in rotation with wheat in soil naturally colonized with B. sorokiniana (Cochliobolussativus). Soil populations of C. sativus under the different rotations were measured at thebeginning of winter and of summer between 1982 and 1986. Populations increased underwheat, barley and triticale, remained static under oats, safflower and chickpea, and declinedunder buffel grass, cocksfoot, lucerne, mung bean, snail medic, sorghum, sunflower andWhite French millet. Populations also declined under a fallow, and propagules of the funguswere still present after 4 years. Where populations had declined owing to cropping history,they were effectively restored to their previous levels after one wheat crop. Severity ofcommon rot in wheat caused by C. sativus was reduced from that occurring with continuouswheat when wheat was planted after safflower, sorghum, mung bean, snail medic, lucerne andbuffel grass. Disease levels in wheat following barley, triticale, oats, chickpea, millet,sunflower, cocksfoot or a fallow were not significantly different from that of continuouswheat. When a second wheat crop was planted, severity of common root rot was high in alltreatments, irrespective of the previous cropping history. The implications of these findings indeveloping control strategies for common root rot by crop rotation are discussed.

121

Mullenax, C.H. (1979): The use of jackbean (Canavalia ensiformis) as a biological controlfor leaf-cutting ants (Atta spp.). Biotropica 11:313-314.

Keywords: leaf-cutting ants; Canavalia ensiformis; insect-plant interaction; biological control;insect pests; South America; Colombia.

Abstract. Savanna-dwelling leaf-cutting ant colonies (Atta spp.) in the Department of Meta,Colombia, were offered freshly cut leaves of jackbean (Canavalia ensiformis) during the rainyseason. Five to 15 kg of leaves were placed nightly on top of and around mounds covering anarea of 25 to 100 m2 for three consecutive nights. A single three-night "treatment" usuallyresulted in complete cessation of ant activity for periods ranging from four months to fiveyears. It is presumed that the effect of jackbean on leaf cutting ant colonies is due to the actionof fungicides contained in jackbean leaves on the ants' fungus gardens.

122

Panizzi, A.R. (1992): Performance of Piezodorus guildinii on four species of Indigoferalegumes. Entomologia Experimentalis et Applicata 63:221-228.

Keywords: legumes; insect pests; soybeans; South America; Indigofera hirsuta; Piezodorusguildinii; Indigofera endecaphylla; Indigofera suffruticosa; Indigofera truxillensis; Brazil;biological control; pest control.

Abstract. The performance of the pentatomid Piezodorus guildinii, a major pest of soybean inSouth America, on 4 species of Indigofera was tested in the laboratory at 25°C, 65% RH and


LD 14:10. Nymphal survival was 88, 15, 70 and 40% on I. endecaphylla, I. suffruticosa, I.hirsuta and I. truxillensis, resp. The fastest development (22 days) from the 2nd to the 5thinstar occurred on I. endecaphylla and I. truxillensis, and the slowest (29 days) on I.suffruticosa. Fresh body weight at emergence was highest for nymphs fed on I. endecaphyllaand I. truxillensis. Adult survival of P. guildinii after 40 days was >70% on I. truxillensis andI. endecaphylla, and <20% on I. suffruticosa. Females oviposited on all Indigofera species,but <30% were observed to lay eggs on I. suffruticosa. Body weight gain during the 1st weekwas greater for adults feeding on I. endecaphylla and I. hirsuta. Insects lost weight on I.suffruticosa; at the end of day 15 no differences in percentage change in body weight amongthe food plants tested were observed. Field surveys conducted on I. truxillensis and I.suffruticosa, the 2 most abundant species in northern Paraná, indicated a greater number ofnymphs, adults and egg masses on the former host. On both hosts, P. guildinii was moreabundant during April-May, after soybean harvest, suggesting movement of the populationsfrom soybean to Indigofera.

123

Sutherst, R.W., Wilson, L.J., Reid, R. and Kerr, J.D. (1988): A survey of the ability oftropical legumes in the genus Stylosanthes to trap larvae of the cattle tick, Boophilusmicroplus (Ixodidae). Australian Journal of Experimental Agriculture 28:473-479.

Keywords: cattle; Stylosanthes viscosa; Stylosanthes scabra; Stylosanthes guianensis;Boophilus microplus; insect-plant interaction; animal-plant interaction; pastures.

Abstract. Stylosanthes viscosa and S. scabra cvv. Fitzroy and Seca have previously beenshown to trap host-seeking larvae of the cattle tick Boophilus microplus and could provide ameans of controlling cattle ticks in improved pastures. We assessed the ability of 229accessions from 22 species of the genus Stylosanthes to trap larvae of B. microplus or toprevent them from ascending plant stems. The 3 species that were most effective wereS.viscosa, S. scabra and S. guianensis. Only accessions which produced sticky secretions wereable to trap tick larvae, but the extend of this ability was related primarily to the density andlength of bristles on the stems rather than to the degree of stickiness. The highest percentageof larvae were trapped when stylo stems had short, dense bristles of average stickiness or longsticky bristles of average density. These features were also most effective at preventing larvaefrom ascending stems. A high density of fine, non-glandular hairs, in conjunction withaverage stickiness, also prevented larvae from ascending stems.

124

Staver, C. (1989): Shortened bush fallow rotations with relay-cropped Inga edulis andDesmodium ovalifolium in wet central Amazonian Peru. Agroforestry Systems 8:173-196.

Keywords: fallow; Inga edulis; Desmodium ovalifolium; Peru; trees; rice; weeds; naturalfallow; cassava; yields; establishment; regeneration; shrubs.

Abstract. In the Palcazu Valley alluvial Inceptisols are relay-cropped with maize-cassava-plantain in rotation with 2-5 years of tree fallow. These lands, of limited extent, yet importantfor Yanesha Indian subsistence production, are being cropped even more intensively aspopulation increases and land is converted to other uses. The relay-planting of the tree-thicketcombination Inga edulis with Desmodium ovalifolium into the on-farm crop sequence wasevaluated as a means to accelerate fallow recovery and thereby shorten fallow rotations. Three

References 93

experiments with Inga/Desmodium planted with cassava-plantain and one with rice underdifferent weeding regimes after a Desmodium fallow were conducted. Inga and Desmodiumwere not chopped back or pruned during these experiments. Desmodium/Inga suppressedherbaceous weeds from one year after planting. Desmodium/Inga accumulated more woodybiomass than natural fallows. Cassava yields were unaffected by the presence ofDesmodium/Inga, while plantain yields were greater under Desmodium/Inga compared tonatural weeds. Desmodium/Inga, while promising for shortening fallow rotations,demonstrated potential difficulties; increased labor for establishment, tendency of Desmodiumto weediness in later crop cycles, and suppression of the natural regeneration of trees andshrubs.

125

Budelman, A. (1988): The performance of the leaf mulches of Leucaena leucocephala,Flemingia macrophylla and Gliricidia sepium in weed control. Agroforestry Systems 6:137-145.

Keywords: mulch; Leucaena leucocephala; weed control; Gliricidia sepium; Flemingiamacrophylla.

Abstract. The performance of leaf mulches of Leucaena leucocephala, Gliricidia sepium andFlemingia macrophylla in weed control has been tested in two trials. The length of the periodduring which a mulch layer yields significantly less weed biomass compared to the controlplots is called the 'effective life-span' of the mulch. Of the three mulch materials only that ofF. macrophylla shows promise in retarding weed development. In the second trial F.macrophylla leaf mulch was applied at rates of 3, 6 and 9 tons dry matter per ha. The effectivelife-span of a mulch layer of 3 tons is between 12 and 13 weeks. The treatments 6 and 9 tonshave effective life-spans of over 14 weeks. For moderate quantities (up to 5 tons of dry leafmulch per ha) the effective life-span is estimated at about 100 days. The value of mulching inweed control is limited to the control of weed species that multiply by seed. Regrowthoriginating from roots or stumps from former vegetation is unlikely to be checked by a mulchlayer.

126

Chou, C.H. (1988): Effects of pasture-forest interaction in Taiwan. In: Allen, P. and vanDusen, D. (eds.), Global perspectives on agroecology and sustainable agricultural systems:Proceedings of the sixth international scientific conference of IFOAM. Santa Cruz:Agroecology Program, University of California, p. 327-340.

Keywords: deforestation; grasses; weeds; allelopathy; Pennisetum clandestinum; agroforestry;tropical highlands.

Abstract. A possible allelopathic interaction of a pasture-forest intercropping system wasevaluated by experiments conducted in field and laboratory assays. After deforestation ofCunninghamia lanceolata (Chinese fir), a split plot design of four treatments (litter removed,litter retained, litter removed and kikuyu grass planted, and litter retained and kikuyu grassplanted) was imposed. Field experiments showed that fir litter left on the ground only slightlyinhibited the growth of weeds in the first four months after deforestation, while kikuyu grasssignificantly suppressed the growth of weeds longer than four months. Both fir litter andkikuyu grass did not reduce growth of fir seedlings. Aqueous extracts of fresh fir leaves, fir


litter, and kikuyu leaves were bioassayed by lettuce and rice seeds and stolon cuttings ofBrachiaria mutica. Bioassays showed that fresh fir leaves produced significant phytotoxicitywhile fir litter and kikuyu grass revealed limited toxicity. Nine phytotoxic phenolics and manyunidentified flavonoids were found in the plant materials. A good correlation between thedegree of phytotoxicity and phytotoxins was established, indicating that allelopathicmechanisms may contribute to the interaction of forest-pasture intercropping systems, thuspotentially reducing the need for herbicides and lessening the labour cost of weed control.Experiments were also conducted to evaluate the competitive and allelopathic nature of covergrasses. Results showed that among nine leachates of grass soils, only four of the leachates(Dactylis glomerata, Bromus catharticus, Lolium multiflorum and Eragrostis curvula)stimulated growth of pear. The growth performance of cover grasses, namely rescue grass,kikuyu grass, Italian rye grass, orchard grass and white clover was compared. Kikuyu grassand white clover grew more agressively than the others; however, when the two grasses grewtogether, white clover invaded the kikuyu grass plot faster than the kikuyu grass invaded thewhite clover plot. This finding suggests that biochemical interactions such as allelopathy maybe involved.

127

Lenné J.M. (1989): Evaluation of biotic factors affecting grassland production - history andprospects. Proceedings of the XVI International Grassland Congress, Nice (France), p. 1811-1815.

Keywords: grassland; pastures; diseases; grasses; legumes; grazing; pests; weeds.

Abstract. This paper summarizes trends in research on biotic factors affecting grasslandproduction with respect to papers presented at International Grassland Congresses during thepast twenty years and discusses problems associated with evaluation of biotic factors indiverse perennial pastures. The number of papers on biotic factors has grown impressivelysince 1970 reflecting increasing awareness among pasture scientists of the importance ofbiotic factors to grassland production. Of particular note is the increased emphasis on diseasesof tropical pasture plants and the new and rapidly developing studies of endophytes intemperate grasslands. Biotic factors affecting mixed grassland communities are difficult toevaluate. Much existing methodology has been only slightly modified from that used for grassand legume monocultures. Limited appropriate evaluation methodology has been developedfor dynamic heterogenous perennial pastures. Initial evaluation in small monoculture plots isusually done in the absence of grazing animals. Use of associated species and simulatedswards which may be grazed, however, is more relevant to the pasture environment. Surveysprovide valuable information on disease, pest and weed incidence and distribution undergrazing. Transects, strategically rather than randomly placed quadrats and marked plants areuseful techniques for measuring biotic factors severity and sampled plants facilitate evaluationof reaction to individual factors. The importance of long-term periodic evaluations of bioticfactors affecting the seedling component of perennial pastures to the understanding of changesin productivity and persistence is emphasized. Determination of economic loss by measuringdecreases in pasture yield and quality and changes in botanical composition provides anassessment of potential animal losses only. Knowledge of the direct effect of pasture diseaseson animal production is necessary for deciding whether control strategies are needed. Thecomplexity of the diverse perennial pasture environment with its potential for multipleinteractions between biotic and environmental factors necessitates a multidisciplinaryapproach to evaluation. Development of general evaluation methodology which can be readily

References 95

modified and applied to specific problems will foster imaginative and efficient approaches toevaluation. Plant population biology techniques, already greatly utilized in weed evaluation,have considerable application to studies of grassland pathogens and pest. More on-farmevaluation of the importance of diseases, pests and weeds to perennial pasture production andpersistence is needed.

128

Chaluat, M.M. de and Perris, S. (1994): Hongos patógenos en semillas de especiesforrajeras tropicales. Pasturas Tropicales 16(1):41-43.

Keywords: seeds; grasses; Chloris gayana; legumes; Leucaena leucocephala; Glycine wightii;diseases; Panicum; Paspalum; introduced species.

Abstract. The most common seed-borne fungi of several introduced forage species inArgentina were identified and their level of incidence established by the PhytopathologyLaboratory, Faculty of Agronomy, University of Buenos Aires. To identify these fungi, 400seeds of each species were placed on filter paper and incubated at 20+3°C in alternate cyclesof 12 hours each of light and darkness. In grass seeds, the most common fungi were (1) inPanicum: Phoma sp., Fusarium, Alternaria, and Epicoccum; (2) in Setaria anceps:Cladosporium, Phoma, and Fusarium; (3) in Chloris gayana: Drechslera sorokiniana,Drechslera sp., and P. sorghina; and (4) in Dichanthium aristatum and Paspalum urvillei:Phyllosticta sp., Curvularia sp., and Drechslera sp. In legume seeds, the most common fungiwere (1) in Leucaena leucocephala: Cladosporium cladosporioides; (2) in Dolichos lablab:Aspergillus, Penicillium, and Fusarium; and (3) in Glycine wightii: Aspergillus flavus,Curvularia sp., and Penicillium sp.

129

Lenné, J.M. and Stanton, J.M. (1990): Diseases of Desmodium species - a review. TropicalGrasslands 24:1-4.

Keywords: Desmodium ovalifolium; pastures; nematodes; fungal diseases; Meloidogyne spp.;diseases.

Abstract. Fungal pathogens representing 36 genera and over 70 species, one bacterium,mycoplasma-like-organisms, at least six viruses, five races of root-knot nematodes and sixother nematodes have been recorded on 18 Desmodium species of agronomic interestthroughout tropical regions. Although limited information precludes a definitive discussion ofthe relative importance of many diseases, 2 fungal diseases - Synchytrium desmodii andPhanerochaeta salmonicolor - causing wart and pink disease, respectively, of Desmodiumovalifolium and several nematode pathogens including races of the root-knot nematodesMeloidogyne arenaria, M. hapla, M. incognita and M. javanica of Desmodium species andstem gall nematode Pterotylenchus cecidogenus of D. ovalifolium are presently regarded asimportant pathogens. Awareness of the range and distribution of fungal pathogens recorded onDesmodium species as well as the existence of potentially seed-borne bacteria and potyvirusesis regarded as essential for preventing global transmission of these pathogens and seriousdisease problems in the future. This is the first time that the great diversity of informationavailable on diseases of Desmodium species has been summarized. It should provide a usefulreference for many tropical pasture scientists.


130

Stanton, J.M., Siddiqi, M.R. and Lenné, J.M. (1989): Plant-parasitic nematodes associatedwith tropical pastures in Colombia. Nematropica 19:169-175.

Keywords: nematodes; pastures; Colombia; legumes; Pueraria phaseoloides; grasses; Arachispintoi; Hyparrhenia rufa; Stylosanthes.

Abstract. A survey of 3 regions of Colombia revealed a total of 31 species of plant-parasiticnematodes associated with tropical pasture legumes and grasses. Seventeen of these nematodespecies had not been recorded previously in Colombia. There were also newly reportedassociations of plant-parasitic nematodes on tropical pasture legumes and grasses. Thenematode species found most commonly and abundantly were Helicotylenchus spp.,Pratylenchus spp. especially P. brachyurus, Monotrichodorus monohystera and Xiphinemaspp. The plant species surveyed were Andropogon gayanus, Arachis pintoi, Brachiaria spp.,Centrosema spp., Desmodium spp., Hyparrhenia rufa, Melinis sp., Pueraria phaseoloides,Stylosanthes spp., and Zornia sp.

131

Martínez-Mojena, A. and Medina, N. (1989): Los insectos como enemigos de los pastos yforrajes. Su combate. Pastos y Forrajes 12:199-207.

Keywords: insect pests; pests; pest control; biological control; pastures; legumes; grasses;insects; rotational grazing; Leucaena leucocephala.

Abstract. This paper presents the most important insect pests of pastures in Cuba. Possibilitiesof integrated pest management, including biological control and control by rotational grazing,are outlined.

132

Calderón C., M. (1981): Insect pests of tropical forage plants in South America. Proceedingsof the XIV International Grassland Congress, Lexington (USA), p. 778-780.

Keywords: insect pests; South America.

Abstract. The objectives of this continuing research are to make a general survey of the insectpopulations occurring in tropical forage plants in South America and to identify the mostimportant pests. To realize this investigation, pure stand plots 5 x 5 m were sampled every 14days during 2 years using a D-Vac vacuum sampler. The following information was obtained:- Most important families and/or genera of insects in tropical forage legumes and grasses. -Insect group frequency for each season. - Insect group frequency for each plant ecotype understudy. - Preliminary data on insect preference. - Preliminary data on relationships betweeninsects on forage plants and viral, fungal and bacterial diseases. - Most important pests inSouth America. The important pests include stemborer (Caloptilia sp.), leafhoppers(Cicadellidae, several genera), and leafeating beetles (Crisomelidae, several genera).Chinchbug (Pentatomidae, Lygaeidae) and sucking planthoppers (Membracidae) are underinvestigation as disease vectors; seed-eating beetles (Curculionidae) and budworms (Stegastabosqueella) reduce seed production. In grasses, spittlebug (Zulia, Aeneolamia, and Deois spp.)causes serious damage, and seed-feeding leafhoppers (Cicadellidae) reduce seed production.This ongoing research provides essential information about the most important insect pests,pests of secondary importance, potential pests, and beneficial insects of tropical forage plants

References 97

in five countries in South America. This is the first complete study of the insect fauna oftropical forage plants, so it is an important one.

133

Wallace, M.M.H. (1970): Insects of grasslands. In: Moore, R.M. (ed.), Australian grasslands.Canberra: Australian National University Press, p. 361-370.

Keywords: grassland; pastures; insect pests; insect-plant interaction.

Abstract. Most of the insect pests of pastures and grazing lands in Australia are indigenous.Populations of some native insects have increased enormously as agricultural and pastoralactivities have modified their environments and raised their food levels. Small numbers ofintroduced insects have also found the changed conditions favourable and, in the absence ofsome or all of their natural enemies, have reached pest proportions in some places. In thetropics and sub-tropics, where the establishment of highly productive pastures is relativelyrecent, insects are not generally deleterious to grassland production. But new species ofgrasses and legumes are being introduced and it would be surprising if some of the nativeinsects and mites now able to sustain only low numbers in the near-original environment donot increase as a result of higher levels of pasture production. This chapter describes the waysinsects or mites affect botanical composition and growth of pastures and attempts to showhow man's agricultural activities create and aggravate insect pest problems. Only thecommoner and more important species are discussed.

134

Fowler, H.G. and Saes, N.B. (1986): Dependence of the activity of grazing cattle on foraginggrass-cutting ants (Atta spp.) in the southern Neotropics. Journal of Applied Entomology101:154-158.

Keywords: cattle; grasses; grassland; Brazil; Paraguay; leaf-cutting ants; insect pests; pastures.

Abstract. In Paraguayan and Brazilian pastures with the grass-cutting ants, Atta bisphaerica,A. capiguara, A. laevigata and A. vollenweideri present, cattle were found to limit theirgrazing activity to areas in which grass-cutting ants were not actively cutting. Cattle confinedto areas in which grass-cutting ants were actively cutting grazed significantly less and walkedsignificantly more than cattle confined to areas free of cutting ants. Forage offered to cattle inwhich workers of grass-cutting ants were placed was consumed significantly less than controltreatments, suggesting that the thoracic spines, which are well developed in Atta spp., may beadaptive in the defense of vegetative resources against large mammalian herbivores, as well asserve other assumed adaptive functions. These results suggest that the impact of grass-cuttingants on Neotropical cattle production is more complex than estimates on their grazingpotential indicate.

135

Schultze-Kraft, R. (1994): El "psyllid" de Leucaena también puede ser un problema enAmérica tropical. Pasturas Tropicales 16(2):48-50.

Keywords: South America; Asia; insects; insect pests; pests; biological control; Colombia;Leucaena leucocephala; Heteropsylla cubana.


Abstract. A brief account of the Leucaena psyllid Heteropsylla cubana, its damage to L.leucocephala and economic importance in Southeast Asia, and the research steps taken to finda solution to the problem is presented. In tropical America, the Leucaena psyllid has not beenconsidered to be an insect pest of major importance because of natural biological control,apparently mainly through predators. However, significant damage and economic loss havebeen observed on farms in the Valle del Cauca department, Colombia. Damage can beparticularly severe during the dry season when psyllid infestation leads to wilting and death ofshoots, with subsequent interruption of foliage production and, when defoliation coincideswith another severe stress, even to the death of otherwise drought-resistant plants. Further,intensified monitoring of the psyllid situation in tropical America is suggested and a series ofresearch steps is recommended.

136

Abramsky, Z. (1983): Experiments on seed predation by rodents and ants in the Israeli desert.Oecologia 57:328-332.

Keywords: seeds; deserts; pests; granivory; ants; rodents.

Abstract. Utilization of non-native seeds by seed-eating rodents and ants was studiedexperimentally in the field. It was found that patterns of granivory in the Israeli deserts arevery similar to those reported for the same groups in the deserts of North America. Rodentsare more efficient than ants at finding and harvesting seeds. Only rodents can find and harvestseeds that occur below the soil surface. The two taxa appear to rank barley particles on thebasis of size. Big seeds are utilized first and the shift to small seeds occurs only after most ofthe big seeds have been utilized. This result agrees with the prediction of optimal diet theory.

137

Ofuya, T.I. and Bamigbola, K.A. (1991): Damage potential, growth and development of theseed beetle, Callosobruchus maculatus (Fabricius) (Coleoptera: Bruchidae), on some tropicallegumes. Tropical Agriculture (Trinidad) 68:33-36.

Keywords: legumes; seeds; Coleoptera; Callosobruchus maculatus; pest development.

Abstract. The damage potential, growth and development of Callosobruchus maculatus oneight different tropical legumes was investigated under laboratory conditions in Akure,Nigeria. One or more larvae of C. maculatus caused significant weight loss in single seeds ofpigeon pea (>14%), cowpea (>10%), soya bean (>5%) and African Yam bean (>3%), whereastwo or more larvae caused significant weight loss in a Bambara groundnut seed (>4%). C.maculatus did not grow and develop on the seeds of winged bean and mucuna bean and only afew adults could be reared from lima bean. Developmental period was longer in soya bean andAfrican yam bean than in Bambara ground nut, pigeon pea and cowpea. The heaviest femaleswere reared from seeds of Bambara groundnut and the lightest from soya bean. Females rearedfrom Bambara groundnut were most fecund and lived longest.

138

McFadden, M.W. (1988): The Leucaena psyllid: An ecological catastrophe. Healthy Forests,Healthy World: Proceedings of the 1988 Society of American Foresters National Convention,Rochester, New York, October 16-19, p. 321-323.

References 99

Keywords: Asia; pests; Leucaena leucocephala; Heteropsylla cubana.

Abstract. In conclusion, the author points out that although the biological time bombrepresented by the broadly distributed, narrow genetically based leucaena exploded over afantastically large geographical area with devasting effects on agricultural economies, theresponse by the scientific community in SE Asia was equal to the task. From the first meetingin Hawaii in November, 1986 until August, 1987, a mere 10 months, five national IPM planshad been developed and a national coordinator selected to coordinate research activities ineach country. A regional IPM plan had been prepared and approved and a regional coordinatorselected to insure integration of research activities across the region. The regioanl IPM planmay be the largest multi-country effort ever developed to coordinate and integrate research ona major pest problem and it offers considerable promise for resolution of the psyllid problem.

139

Lenné, J.M., Vargas, A. and Torres, C. (1985): Damaging fungal diseases of promisingpasture legumes in the tropical American lowlands. Proceedings of the XV InternationalGrassland Congress, Kyoto (Japan), p. 807-809.

Keywords: fungal diseases; diseases; legumes; disease resistance; pastures; Stylosanthes spp.;Centrosema brasilianum; Zornia latifolia; Desmodium ovalifolium; nematodes; Colombia;adapted germplasm.

Abstract. The most damaging fungal diseases in pasture legumes in the major ecosystems ofthe tropical American lowlands are discussed. Detailed evaluations during the past seven yearsin major screening sites and more than 100 RIEPT sites have identified more than 30 diseasesof tropical pasture legumes caused by fungi, bacteria, mycoplasmas, viruses and nematodes.Of these, four fungal diseases are the most damaging: Anthracnose caused by Colletotrichumspp., is the most widespread and damaging disease of Stylosanthes. Dry matter losses of 26 to100% have been recorded in several species. Foliar blight caused by Rhizoctonia solani is alsowidespread; 10 to 30% dry matter losses have been recorded in Centrosema brasilianum inColombia. Dry matter losses of 55% have been recorded in Zornia latifolia by Sphacelomazorniae, the causal agent of scab, while false rust, caused by Synchytrium desmodii, hascaused considerable damage to Desmodium ovalifolium in Colombia. Resistance, the mostpractical and economic management approach, is being sought to these diseases in an on-going multi-disciplinary, multi-institutional and multi-locational screening and selectionresearch strategy. Understanding of the plant, pathogen, environment and their interactions isconsidered essential to effective evaluation and utilization of selected resistance.

140

Lenné, J.M. and Trutmann, P. (eds.) (1994): Diseases of tropical pasture plants.Wallingford, Oxon, UK: CAB International, 404 p.

Keywords: diseases; pastures; legumes; grasses; nematodes; Australia; USA; South America;Asia; Africa.

Abstract. Increasingly, diseases are being identified as major constraints to the productivityand persistence of improved tropical pastures. This book provides a comprehensive review ofdiseases of tropical pasture legumes and grasses. After an introductory chapter, nine chaptersreview the main fungal, bacterial and mycoplasma diseases and a further two consider viraland nematode diseases of legumes and grasses such as Stylosanthes, Centrosema,


Desmodium, Leucaena and Andropogon. Five chapters then describe regional experience inAustralia, the Southern USA and Caribbean, Central and South America, Southeast Asia andthe Pacific, and Africa. The final part of the book covers general management of diseases,molecular techniques for characterization and diagnosis of pathogens, and internationalcooperation and future research. The book represents a comprehensive, fully referencedsourcebook for plant pathologists and pasture agronomists.

141

Lenné, J.M., Thomas, D., Andrade, R.P. and Vargas, A. (1984): Anthracnose ofStylosanthes capitata: implications for future disease evaluations of indigenous tropicalpasture legumes. Phytopathology 74:1070-1073.

Keywords: pastures; legumes; Colombia; Brazil; Stylosanthes capitata; South America; fungaldiseases; Colletotrichum gloeosporioides; disease resistance.

Abstract. During field screening from 1978 to 1981 of 121 accessions of the tropical pasturelegume Stylosanthes capitata at two sites in Colombia and at Planaltina in Brazil, 94.2% ofthe accessions were resistant to anthracnose (caused by Colletotrichum gloeosporioides) inColombia while 85.1% were susceptible in Brazil. In comparative seedling pathogenicitystudies with isolates from both countries, isolates pathogenic to a wide range of accessions ofS. capitata were only found in Brazil. Results strongly suggest that specialized isolates of C.gloeosporioides pathogenic to S. capitata exist in Brazil (the native habitat and probablecenter of diversity of this legume) and not in Colombia where S. capitata is an exotic species.This implies the need to screen indigenous tropical pasture legumes for desease resistance intheir native habitats and the need for international collaborative disease screening trials in thefuture.

142

Lenné, J.M. (1989): Problems associated with evaluation of diseases of perennial pastureplants - some recommendations. Proceedings of the XVI International Grassland Congress,Nice (France), p. 695-696.

Keywords: diseases; pastures; evaluation methods; yields.

Abstract. The complexity of the perennial pasture environment, the potential for multipleinteractions between pathogens and pests, as well as environmental factors, and the grazinganimal, necessitates a multidisciplinary approach. Techniques used in plant populationbiology have great application to pasture pathology. More information is required on thepractical importance of diseases at the farm level and the effect of diseases on perennialpasture plants over time. Diseases can greatly affect plant persistence, evaluation of which isessential to any determination of whether diseases cause significant reduction in animalproduction and whether control strategies are needed. (Abstract by bibliography authors)

143

Toledo, J.M. and Nores, G.A. (1986): Tropical pasture technology for marginal lands oftropical America. Outlook on Agriculture 15:2-9.

Keywords: pastures; marginal lands; low-input technology; adapted germplasm; acid soil.

References 101

Abstract. CIAT's Tropical Pastures Program is concerned with solving the problems of lowproductivity in acid, marginal, and frontier lands by developing new, low-input technologybased on adapted germplasm. Its tropical pasture germplasm collection is the world's largestfor acid soils in tropical humid and sub-humid areas.

144

Scott, D.R. (1970): Feeding of Lygus bugs (Hemiptera: Miridae) on developing carrot andbean seed: Increased growth and yields of plants grown from that seed. Annals of theEntomological Society of America 63:1604-1608.

Keywords: insect pests; insect-plant interaction; seed production.

Abstract. To determine the effect of lygus bugs, Lygus hesperus Knight and Lygus elisus VanDuzee, feeding on developing carrot seed on the plants grown from that seed, adult lygus bugswere caged on carrot umbels. Some of the seed was then germinated and growth of the shootwas measured. Other seed was planted in the field, growth of the plants was measured, andweight of the roots was determined. Bean seed was sorted as to the number of lygus puncturesper seed, then weighed and planted. Growth of the plants and seed yields were determined.Shoot growth from carrot seeds exposed to feeding by lygus bugs during development isreduced and varies inversely with the bug population. Plants grown from such seeds latersurpass plants from seeds protected from lygus bugs during development and produce heavierroots. Bean plants grown from seeds with lygus bug punctures surpassed plants from seeds notfed on by lygus bugs. Although bean seeds were significantly lighter in weight when fed on bylygus bugs, they produced plants which grew significantly faster and yielded significantlyheavier amounts of seed. Three possible explanations are discussed: (1) destruction of aninhibitor (possibly dormin) present in the seed; (2) injection of a plant auxin (possibly beta-indolyl acetic acid) into the developing seed during the feeding process; and (3) change of theprotein-carbohydrate ratio in the seed as a result of feeding by lygus bugs.

145

Dyer, M.I. and Bokhari, U.G. (1976): Plant-animal interactions: Studies of the effects ofgrasshopper grazing on Blue Grama Grass. Ecology 57:762-772.

Keywords: grassland; insect pests; insect-plant interaction; grasses; grasshoppers.

Abstract. Results of a laboratory experiment where we measured the influence ofgrasshoppers (Melanoplus sanguinipes) feeding upon leaves of hydroponically grown bluegrama grass (Bouteloua gracilis) are presented. Performance of both the plant and animalconditions are given: growth rate of the plants held at three temperatures, amount of foodingested by the grasshoppers, digestive efficiencies, weight change of grasshoppers, theamount of litter cut, and the pH change of the root medium. The experiment indicates thatthere are plant processes triggered by grasshopper feeding which result in increased energytransport levels within the plant. Moreover, regrowth potentials of the plants on whichgrasshoppers had been feeding is much higher than for plants that had simply been clipped.Hence, we suggest that perhaps the largest single effect displayed by aboveground insectgrazers on grassland ecosystem plants (viz., grass) is the increase in belowground respirationand root exsudation.


146

Marshall, D.L., Levin, D.A. and Fowler, N.L. (1985): Plasticity in yield components inresponse to fruit predation and date of fruit initiation in three species of Sesbania(Leguminosae). Journal of Ecology 73:71-81.

Keywords: yield components; insect-plant interaction.

Abstract. (1) Changes in the components of yield in response to artificial predation and to dateof fruit initiation were measured in three species of Sesbania. (2) The removal of fruits, whichmimicked damage by chewing insects, resulted in significant changes in seed weight but notin seeds produced per fruit. Injection of alcohol into developing seeds, which mimickeddamage by hemipterans, resulted in selective abortion of more heavily damaged fruits and ofyounger fruits. (3) The nature of the response to predation depended on its timing becauseresponses become less flexible as development proceeds. (4) Differential responses topredation among the species appeared to be related to the investment in seeds versus pods,since S. vesicaria, which had the highest quotient of seed weight to fruit weight, had thehighest rate of fruit abortion. (5) Fruits initiated on later dates were less likely to mature in allthree species. Late fruits had an unchanged number of ovules but reduced seed size in S.macrocarpa (annual), reduced ovule number but unchanged seed size in S. vesicaria (annual),and unchanged ovule number and seed size in S. drummondii (perennial). (6) The differencesamong species in response to date of fruit initiation suggest that each annual species holdsmost constant the yield component most closely related to fitness, while the perennial is lessresponsive to stress because its stored reserves provide a buffer.

147

Kretschmer Jr., A.E., Sonoda, R.M. and Snyder, G.H. (1980): Resistance of Desmodiumheterocarpon and other tropical legumes to root-knot nematodes. Tropical Grasslands14:115-120.

Keywords: forage legumes; nematodes; Florida; breeding; pest resistance; pest control.

Abstract. Carpon desmodium (Desmodium heterocarpon cv. Florida), a long-lived, high seedproducing, perennial tropical forage legume for grazing, was released for commercial use insouth Florida in 1979. It is susceptible to root-knot nematodes (Meloidogyne spp.). Agreenhouse and a field experiment were used to assess root-knot nematode resistance ortolerance of other carpon desmodium accessions, to determine resistance of severalcommercial tropical legumes, and to compare first-season productivity of tropical legumes.Two of eight carpon desmodiums, Desmodium adscendens, greenleaf desmodium(Desmodium intortum cv. Greenleaf), centro (Centrosema pubescens), siratro (Macroptiliumatropurpureum cv. Siratro), stylo (Stylosanthes guianensis cv. Cook), Caribbean stylo (S.hamata cv. Verano), and jointvetch (Aeschynomene americana cv. American) were apparentlyresistant to Meloidogyne spp. No galls were noted on roots of these species from nematodeinfested soil. Moderate to severe galling was found on roots of Florida and four other carponaccessions, and on a Centrosema pascuorum accession. Very slight galling was found on rootsof one carpon desmodium accession and on calopo. Yield and survival of affected plants wereless than those of plants from inoculated or fumigated plots. In the absence of root-knot,yields of the two resistant carpon desmodiums were considerably less than that of Floridacarpon while in the presence of root-knot their yields were significantly higher. Findingnematode resistance in carpon desmodium is encouraging for future selection and breedingprogrammes.

References 103

148

Hardy, S.R.L. (1987): The relationship between Aeschynomene americana L. and root-knotnematodes (Meloidogyne spp.). Dissertation Abstracts International. Section B. The Sciencesand Engineering 48:924B-925B.

Keywords: Aeschynomene americana; nematodes; Meloidogyne spp.; pest resistance;legumes; USA; breeding; Florida.

Abstract. An improvement programme for A. americana was initiated in Florida, USA todevelop desirable agronomic traits and expand its commerical uses. To precisely transfer traitsbetween genotypes an artificial hybridization technique was developed. The method involvedthe removal of the stamens followed by controlled pollination. The risks of self pollination orcontamination were minimized and the success rate was maximized. The success rate was notaffected by the female or male parent used. A population of A. americana genotypes wasindividually examined for their responses to M. incognita race 1 and 3; M. javanica; and M.arenaria race 1. The population was found to contain a wide range of responses from resistantto susceptible. Three plant genotypes with different responses were used to examine theeffects of the genotype on the life cycle of M. incognita race 3 under two different day lengthand temperature regimes. The plants were examined weekly and the different nematode lifecycle stages counted after staining. Development to maturity was reduced in the more resistantgenotypes in both environmental regimes. Under long days and higher temperatures, survivingfemales in resistant genotypes could reproduce as well as those in the susceptible genotypes.Two resistant and 2 susceptible plant genotypes which had uniform nematode responses wereselected for the examination of the genetic system controlling the responses of 3 root-knotnematode species. They were crossed and their first filial generation used to create 2nd filialgenerations and backcrosses. All the generations were tested with each nematode species. Thedata from all the families and generations for the 3 nematode species were combined; thereappeared to be one dominant gene for resistance common to all 3 species. There was evidencefor other genes being involved which seemed to be partially dominant, and probably specificto the individual nematode species.

149

Lamprecht, H. (1977): Structure and function of South American forests. In: Muller, P. (ed.),Ecosystem research in South America. The Hague: Junk, p. 1-15.

Keywords: ecosystems; South America; tropical forest; hydrology; soil erosion; speciesdiversity.

Abstract. The study deals mainly with the tropical evergreen forests and moist forests ofnorthern South America. The basal area of these intensely mixed natural forests with manyspecies reaches its minimum in the tropical tropophytic forest and its maximum in the Andeancloud forest. The curve of diameter distribution is typical of a selection forest. As far asprotective functions are concerned these forests are satisfactory, but their productive functionsare insufficient. The task of forestry is to convert these unproductive natural stands intoproductive commercial forests without decreasing their protective and social functions.

150

Lal, R. (1981): Deforestation of tropical rainforest and hydrological problems. In: Lal, R. andRussell, E.W. (eds.), Tropical Agricultural Hydrology. Chichester: Wiley, p. 131-140.


Keywords: deforestation; hydrology; soil erosion; erosion; Nigeria; shifting cultivation;Pueraria phaseoloides; Stylosanthes guianensis; Centrosema pubescens; tropics.

Abstract. In spite of the adverse environmental consequences, vast areas of tropical forest willhave to be developed for food production. The objectives of this report are to describe theeffects of methods of deforestation and of post-development soil management on runoff rateand amount, sediment density and soil erosion in a tropical catchment in southwest Nigeria.Data presented indicates that other than shifting-cultivation treatment, manually cleared plotsproduce less water runoff and soil loss than using heavy machinery for clearing. To ensuresustained productivity, it is important to develop appropriate soil management systems thatwill minimize the adverse effects of deforestation by mechanical means. Care must beexercized not to remove all roots, stumps and other biomass. Crop covers (such as Puerariaphaseoloides, Stylosanthes guianensis, Centrosema pubescens, etc.) may play an importantrole in the management of soils in the humid tropics.

151

Gentry, A.H. and López-Parodi, J. (1980): Deforestation and increased flooding of theupper Amazon. Science 210:1354-1356.

Keywords: deforestation; watershed; Peru; Ecuador; hydrology; Amazon region; flooding.

Abstract. The height of the annual flood crest of the Amazon at Iquitos has increasedmarkedly in the last decade. During this same period, there has been greatly increaseddeforestation in the upper parts of the Amazon watershed in Peru and Ecuador, but nosignificant changes in regional patterns of precipitation. The change in the Amazonian waterbalance during the last decade appears to be the result of increased runoff due to deforestation.If so, the long-predicted regional climatic and hydrological changes that would be theexpected result of Amazonian deforestation may already be beginning.

152

Nordin, C.F. and Meade, R.H. (1982): Deforestation and increased flooding of the upperAmazon. Science 215:426-427.

Keywords: deforestation; flooding; Amazon region; hydrology.

Abstract. Comment on the report "Deforestation and flooding in the upper Amazon" byGentry and López-Parodi (reference no. 151), who concluded that the height of the annualflood crest of the Amazon at Iquitos has increased during the last decade as a result ofincreased runoff due to deforestation: Nordin and Meade criticize that the aforementionedauthors have considered neither the relation between water discharge and stage nor changes inthe configuration of the sandy stream bed. Also the effects of spatial and temporal distributionof precipitation have not been taken into account. Finally, Nordin and Meade argue that the t-test, used by Gentry and López-Parodi, should not be applied to such hydrologic data.(Abstract by bibliography authors)

153

Dudal, R. and Purnell, M.F. (1986): Land resources: salt affected soils. Reclamation andRevegetation Research 5:1-9.

References 105

Keywords: soil salinity; revegetation; regeneration; improved pastures; silvopastoral systems.

Abstract. Although the world as a whole has enough land to support its projected population,many countries do not have the resources to be self-sufficient in food and fuel. The increase inproduction necessary to meet increasing demand must come from higher yields, intensifiedproduction and development of potentially productive wasteland. Salt affected soils occupyabout 7% of the world's land area. Studies of the distribution, classification and productivepotential of these soils are required to plan their development on a global scale. Achieving thefull potential of salt affected land also requires the consideration of social and economicconditions.

154

Bari, M.A. and Schofield, N.J. (1992): Lowering of a shallow, saline water table byextensive eucalypt reforestation. Journal of Hydrology 133:273-291.

Keywords: reforestation; groundwater level; pastures; water salinity; groundwater; Australia.

Abstract. Land and stream salinisation in Western Australia has occurred as a result of theclearing of native vegetation for agricultural development. One approach to controlling thesalinisation, extensive reforestation, has been tested on a site which was 35% cleared andconverted to pasture in the 1950s. By 1979 saline ground water was discharging in the valleywhere the clearing had taken place. At that time 63 Eucalyptus and two Pinus species wereplanted in 0.5 ha blocks across the site, covering some 70% of the cleared land. Thereforestation has been successful in substantially lowering the saline groundwater table acrossthe site. Over the 1980-1989 period, the average minimum groundwater levels beneathreforestation declined by 5.5 m relative to the ground level and by 7.3 m relative to a nearbypasture control site. After the first 3 years the rate of decline was near-uniform with time. Theaverage salinity of the ground water beneath reforestation decreased by 11%.

155

Bell, R.W., Schofield, N.J., Loh, I.C. and Bari, M.A. (1990): Groundwater response toreforestation in the darling range of Western Australia. Journal of Hydrology 119:179-200.

Keywords: groundwater; reforestation; Australia; deforestation; water salinity; pastures;annual field crops; groundwater level.

Abstract. Replacement of deep-rooted perennial vegetation with annual crops and pastures hasled to rising groundwater tables and transport of previously stored salts to streams insouthwest Western Australia. Trials to determine the potential of various reforestationstrategies to reverse this process by lowering the groundwater table were commenced in 1976-1981. Results are reported from six experimental sites for the period 1979-1986. Despite themean annual rainfall of the experimental period being 10% below the 1926-1986 mean,groundwater levels under pasture rose by up to 1.2 m. The change in groundwater levelsbeneath reforestation ranged from a 0.6-m increase to a 3-m decrease relative to the groundsurface. Groundwater levels under reforestation in all cases decreased relative to groundwaterlevels under pasture. The magnitude of this reduction was shown to increase with theproportion of cleared area reforested and with the crown cover of the reforestation. Thesalinity of the water table decreased by 12% under reforestation and by 32% under pastureover the period 1979-1986.


156

Pereira, C. (1981): Rehabilitating eroded hill lands in the People's Republic of China. WorldCrops 33:96-99.

Keywords: trees; watershed; revegetation; Medicago sativa; soil erosion; reforestation.

Abstract. This is a report of an extensive road tour of active rehabilitation work in 2 seriouslyeroded provinces, Shaanxi and Jiangxi. Methods of restoration were initiated in 1950, butduring the ten years of the Cultural Revolution work was severely set back, with many plantedtrees felled. Rehabilitation of small watersheds is now being resumed on a basis of localinitiative. Restoration by conventional means, including the planting of 15 million trees (100per capita of resident population) and by new technology, applying aerial seeding for therevegetation of bare hills, using 2.25 kg of lucerne (Medicago sativa) seeds/ha are recorded. Inaddition the reafforestation of sub-tropical hills is also discussed.

157

Sharma, P.D. and Minhas, R.S. (1993): Land use and the biophysical environment ofKinnaur district, Himachal Pradesh, India. Mountain Research and Development 13:41-60.

Keywords: India; pastures; livestock; hydrology; reforestation; tropical highlands;overgrazing.

Abstract. The extensive alpine pastures of Kinnaur in the Indian Himalaya are an invaluableresource, with fertile soils that provide high-quality pasturage above treeline. However, todaythese pastures are being degraded by excessive livestock pressure and lack of goodmanagement. This is weakening animal husbandry programs and upsetting the normalhydrological functioning of the upland river catchments. The forested area in the KinnaurDistrict is small and only half is under well protected forest. Within the forest infiltration andwater retention rates are high and help to effect regular sediment-free water yields to therivers, but there is growing pressure from the local people who claim that they need a largeproportion of the annual yield of the forest. The cultivable waste lands that cover a large areashould be used by social forestry to augment the vegetation cover and reduce the pressure onthe present forest land. The cultivated area is limited and produces low yields of lessremunerative crops. The agricultural land in the forest and alpine belts on steep slopes is beingseverely eroded and may become completely unstable.

158

Rechcigl, J.E., Payne, G.G., Bottcher, A.B. and Porter, P.S. (1992): Reduced phosphorusapplication on bahiagrass and water quality. Agronomy Journal 84:463-468.

Keywords: phosphorus; Paspalum notatum; yields; water pollution; soil chemical properties;Florida; fertilization; pastures.

Abstract. Phosphorus is considered to be the major factor causing eutrophication of LakeOkeechobee and other waterways in Florida. An important source of P for Lake Okeechobeeis runoff of soluble P fertilizer applied to bahiagrass (Paspalum notatum Flugge) pastures. Astudy was conducted to ascertain whether P application levels could be reduced below currentagronomic recommendations without affecting pasture yields or quality and to determine theeffects of P application on surface water quality. A field study was conducted on a bahiagrasspasture to assess the yield response of bahiagrass to five annual rates of P (0, 6, 12, 24, and 48

References 107

kg ha-1) and two application times (dry season and wet season). Fertilizer treatments werearranged in a randomized complete block design with four replications on an Immokalee finesand (sandy, siliceous, hyperthermic Arenic Haplaquods). Results indicate that P fertilizationrates could be reduced from 48 to 24 kg P ha-1 without affecting yields or quality ofbahiagrass. Yields in 1989 averaged 11.4, 14.7, and 10.4 Mg ha-1 for the 48, 24, and 0 kg Pha-1 treatments, respectively. Time of P application had no effect on yields or quality ofbahiagrass. There was a linear increase in Mehlich I extractable P in the A and E horizons anda quadratic increase to P in the Bh horizon in 1989. Extractable P ranged from 3.8 to 22.5, 1.3to 2.5, and 21 to 55 mg P kg-1 for the A, E, and Bh horizons, respectively. Phosphorusconcentrations in surface water runoff was reduced from 33 to 60% as P application rateswere decreased from 48 to 12 kg P ha-1 while total P loss was reduced from 17 to 78%,respectively. Recommended reductions in P application should result in substantial costsavings to producers and also reduce P inputs into surface water.

159

Thorburn, P.J., Cowie, B.A. and Lawrence, P.A. (1991): Effect of land development ongroundwater recharge determined from non-steady chloride profiles. Journal of Hydrology124:43-58.

Keywords: groundwater; Australia; pastures; annual field crops; groundwater level;deforestation; soil salinity.

Abstract. The effect of clearing and subsequent crop and pasture growth on recharge toground waters was investigated in three experimental catchments in the brigalow (Acaciaharpophylla) lands of north-eastern Australia. Recharge was calculated from soil chloridedata, using a simple transient solute mass balance model. Clearing had a substantial initialeffect on groundwater recharge, with average recharge rates of 29 to 70 mm year-1 in twocleared catchments, compared with 7 mm year-1 in an uncleared catchment. These results wereattributed to record high rains that fell while both cleared catchments were bare of vegetation,before crops or pastures were established. The effect was only short lived, however, with nosignificant recharge occurring in any of the three catchments during the period in which cropsand pastures were fully established. This lack of recharge was contrary to the general beliefthat clearing and establishment of crops or pastures causes a sustained increase ingroundwater recharge. The low recharge rates at this site were attributed to the slowlypermeable soils and the climate of the study site, where potential evaporation exceeds averagerainfall in all months, and to the water use characteristic of brigalow. Brigalow is shallow-rooted, and at this site generated lower soil water deficits than either crops or pastures.Clearing is unlikely to result in high water-tables in these soils under pastures or opportunitycropping systems under the average climatic conditions of the region. The simple transientsolute mass balance model used to estimate recharge rates gave important and significantdifferences in recharge when compared with a more commonly used steady-state model. Allrecharge rates calculated with the steady-state model were less than or equal to 1.8 mm year-1

(most < 0.3 mm year-1), and so this model could not identify the gross short-term rechargeresponse to clearing at this site.

160

Burrows, W.H. (1991): Sustaining productive pastures in the tropics. 11. An ecologicalperspective. Tropical Grasslands 25:153-158.


Keywords: pastures; Australia; natural grassland; sustainability; ecosystems; degradation; soilsalinity; legume trees; animal production; trees; water salinity.

Abstract. Opportunities for continued utilisation of Australia's tropical pasture systems areexplored and some of the ecological constraints leading to breakdown of the systemsdiscussed. The need to evaluate basic range management concepts for managing the extensiveareas of native and naturalised pastures is highlighted.

161

Shelton, H.M., Lowry, J.B., Gutteridge, R.C., Bray, R.A. and Wildin, J.H. 1991.Sustaining productive pastures in the tropics. 7. Tree and shrub legumes in improved pastures.Tropical Grasslands 25:119-128.

Keywords: pastures; trees; shrubs; Australia; sustainability; Leucaena leucocephala; legumetrees; animal production; silvopastoral systems; agroforestry.

Abstract. Among tropical legumes, the tree species Leucaena leucocephala has demonstrateda high potential for increasing liveweight gain. Expansion of its use is limited by damage fromthe psyllid (Heteropsylla cubana) and the slow rate of establishment of Leucaena seedlings insome environments. These problems with L. leucocephala have given impetus to the searchfor alternative varieties and species of tree legumes with similar features. These featuresinclude longevity and versatility of management once established, high animal productionpotential, tolerance of a wide range of climatic and edaphic environments, and potential for ause in a range of agroforestry applications because of their deep rooted habit. The shadingeffect of tree canopies can have a positive effect on understorey grass yield and quality due toimproved nutrient cycling. There is potential for selection of higher yield, improved psyllidand high temperature tolerance within the Leucaena genus. Other promising genera of treelegumes include Calliandra, Gliricidia, Albizia and Sesbania. However, there are problems oflower nutritive value and acceptance in some of these genera and further evaluation isrequired. Also it is not known how well these other tree legumes can tolerate direct grazing.The future acceptance of tree legumes by graziers will depend on the improved availability ofsuitable germplasm, a practical knowledge of their establishment and managementrequirements, and a clear demonstration of their potential economic benefits.

162

Anderson, G.W., Moore, R.W. and Jenkins, P.J. (1988): The integration of pasture,livestock and widely-spaced pine in South West Western Australia. Agroforestry Systems6:195-211.

Keywords: pastures; livestock; Australia; economics; trees; silvopastoral systems; soil salinity;soil erosion.

Abstract. This paper expands on a short voluntary presentation, by the first two authors, to the18th IUFRO World Congress held at Ljubljana, Yugoslavia, in September 1986. It describesmanagement procedures and incorporates biological and economic data, from a number ofagro-silvo-pastoral trials in the South West of Western Australia. The integration of pinetimber and livestock production is shown to have a range of economic and environmentalbenefits available in the long-term. Ways in which the choice of tree density, planting patternand silvicultural regime can each be directed towards the achievement of various objectivesare indicated.

References 109

163

Jones, R.K., Dalgliesh, N.P., Dimes, J.P. and McCown, R.L. (1991): Sustaining multipleproduction systems. 4. Ley pastures in crop-livestock systems in the semi-arid tropics.Tropical Grasslands 25:189-196.

Keywords: pastures; tropics; farming systems; Australia; legumes; establishment; nitrogen;crop residues; cattle; grasses; leaching; sustainability; ley farming.

Abstract. The search for economically viable ley pastures in the Australian tropics is anattempt to emulate the successful ley farming systems, based on subclover and wheat, inregions with Mediterranean and temperate climates in southern Australia. The paper examinesexperimental legume ley pastures in the semi-arid tropics from four points of view, viz., initialestablishment and reestablishment of the various ley species after a crop; the contribution ofbiological nitrogen from the ley to the farming system; the control of pasture species duringcrop phase; and the feeding value of ley pastures and crop residues to grazing cattle.Management problems highlighted by the research on experimental ley pastures include: grassdominance in the pasture; the extremely rapid decomposition of legume residues and theresultant leaching of mineral nitrogen beyond the root front of the developing crop; and thelack of sufficient crop and pasture residues in some seasons for successful crop establishmentusing no-till methods. The adequacy of existing genetic resources for ley pastures in thisregion, the biological and economic sustainability of tropical ley systems, and the prospectsfor commercial use of the experimental results, are also examined.

164

Dregne, H.E. (1992): Rehabilitating degraded arid lands: options and decisions. Problems ofDesert Development 3:19-22.

Keywords: degradation; grazing; stocking rate; rangeland; marginal lands; regeneration;improved pastures; economics.

Abstract. Land degradation affects three-quarters of the global grazing land, about half of therainfed cropland, and about a quarter of the irrigated land. Reclamation of irrigated land iscost-effective for almost all of such land. It is believed to be cost-effective on about two-thirdsof the rainfed cropland and no more than half of the grazing land. Since there is no socially orpolitically acceptable way to reduce stocking rates on marginal rangelands or to preventcultivation of unfavorable croplands by government edict, ways must be found to bring aboutvoluntary reduction of land pressures. The proposal presented in the paper is to concentrateresources on improved conservation and production on better lands. Little or nothing shouldbe spent on improving marginal lands. In time, the need to exploit marginal lands woulddecrease, allowing them to recover, albeit slowly.

165

Herrera, M.A., Salamanca, C.P. and Barea, J.M. (1993): Inoculation of woody legumeswith selected arbuscular mycorrhizal fungi and rhizobia to recover desertified Mediterraneanecosystems. Applied and Environmental Microbiology 59:129-133.

Keywords: legumes; ecosystems; revegetation; shrubs; desertification; degradation;mycorrhiza; rhizobia.


Abstract. Revegetation strategies, either for reclamation or for rehabilitation, are being used torecover desertified ecosystems. Woody legumes are recognized as species that are useful forrevegetation of water-deficient, low-nutrient environments because of their ability to formsymbiotic associations with rhizobial bacteria and mycorrhizal fungi, which improve nutrientacquisition and help plants to become established and cope with stress situations. A range ofwoody legumes used in revegetation programs, particularly in Mediterranean regions, wereassayed. These legumes included both exotic and native plant species and were used in a testof a desertified semiarid ecosystem in southeast Spain. Screening for the appropriate plantspecies-microsymbiont combinations was performed previously, and a simple procedure toproduce plantlets with optimized mycorrhizal and nodulated status was developed. The resultsof a 4-year trial showed that (i) only the native shrub legumes were able to become establishedunder the local environmental conditions (hence, a reclamation strategy is recommended) and(ii) biotechnological manipulation of seedlings to be used for revegetation (by inoculationwith selected rhizobia and mycorrhizal fungi) improved outplanting performance, plantsurvival, and biomass development.

166

Nepstad, D.C., Uhl, C. and Serrão, E.A.S. (1991): Recuperation of a degraded Amazonianlandscape: forest recovery and agricultural restoration. Ambio 20:248-255.

Keywords: grasses; trees; agroforestry; Brazil; deforestation; reforestation; Anacardiumoccidentale; Bixa orellana; Byrsonima crassifolia; Bertholletia excelsa; Spondias mombin;Swietenia macrophylla; Cedrela odorata; Stryphnodendron pulcherrimum; fruit trees; tropicalforest; pastures; degradation; sustainability; Amazon region.

Abstract. Ranching and logging operations are transforming the moist tropical forests of theeastern Amazonian landscape into a mosaic of pastures and regrowth forests. The process isillustrated by reference to the Paragominas region of Pará state, an area which has beenranched and logged for >20 yr. The new ecosystems of this region are agriculturallyunproductive, biologically impoverished, and far more inflammable than the mature foreststhey replace; hydrological differences between the new and old systems are unknown andpotentially large. In the absence of fire, the forest regrows on abandoned sites, accumulatingbiomass and species at a rate that is inversely related to the intensity of use prior toabandonment. Forest regrows slowest on those rare abandoned pastures that were oncescraped with bulldozers. The grass- and shrub-dominated old fields that form on some of thesesites resist forest regrowth because of numerous barriers to tree establishment and growth.These barriers have been studied in detail in an old field at Fazenda Vitoria (Vitoria Ranch),6.5 km NW of Paragominas town, and include low propagule availability, seed and seedlingpredation, seasonal drought, and root competition with old field vegetation. Knowledge ofthese barriers provides a basis for developing inexpensive techniques (1) to restoreagricultural productivity in old fields by planting tree-based agricultural systems or (2) torestore forest regenerative capacity in old fields by establishing trees that attract seed-carryinganimals and ameliorate harsh environmental conditions. The first technique (an agroforestryoption) has been used by Brazilian farmers of Japanese descent and involves planting fruit,nut and timber tree seedlings, whose growth may be enhanced by establishing them in a holefilled with loose soil and decaying organic matter in a weed-free area of 50-cm radius. Usingthis planting method at Fazenda Vitoria promoted fruiting of several species within 1 yr ofplanting (e.g. Anacardium occidentalis [A. occidentale], Bixa orellana and Byrsonimacrassifolia). Slower growing fruit and nut trees were robust 2 yr after planting (e.g.

References 111

Bertholletia excelsa and Spondias mombim [S. mombin]) and even some timber speciesexceeded 4 m in height (e.g. Swietenia macrophylla and Cedrela odorata). The secondtechnique involves planting 'island-forming' tree species that grow rapidly in full sun andproduce fleshy fruits soon after planting, preferably establishing them at short intervals fromthe forest edge to the centre of the old field, so that seed carrying animals penetrate far into theold field. An example of such a species is Stryphnodendron pulcherrimum. These restorationtechniques will be needed over large areas of Amazonia if current attempts to reform degradedpastures fail.

167

Uhl, C., Buschbacher, R. and Serrão, E.A.S. (1988): Abandoned pastures in easternAmazonia. I. Patterns of plant succession. Journal of Ecology 76:663-681.

Keywords: pastures; degradation; Amazon region; South America; tropical forest;reforestation.

Abstract. (1) Vegetation composition, structure, and biomass accumulation were studied onthirteen forest sites that had been cut and burned, used as cattle pastures, and then abandonedin the eastern Amazon near Paragominas, Pará, Brazil. (2) The study sites were of two ages(two to four years and seven to eight years) and had received light, medium or heavy use forup to thirteen years. (3) Forest regenerated vigorously on sites of previously light use. Above-ground biomass accumulation averaged 10 t ha-1 yr-1 or 80 t after eight years (roughly one-quarter of mature forest levels). Tree species richness was also high (about 20 per 100 m2) andalmost all species also occurred in native forest. Moderately grazed pastures also developedforest but biomass accumulation was only 5 t ha-1 yr-1 . Tree species richness was also lowerthan on light-use sites and there were fewer forest trees. Abandoned pastures subjected toheavy use had the least distinct patterns of succession. The single eight-year-old site wasdominated by grasses and forbs with fewer than one tree per 100 m2 and an above-groundbiomass accumulation of 0.6 t ha-1 yr-1 , a value only about 6% of that found on light-use sites.(4) The light-use sites had significantly higher biomass and species richness in both age-classes than either moderate- or heavy-use sites. Site age was a good predictor of above-ground biomass accumulation on light- and moderate-use sites, but not on heavy-use sites. (5)These Amazon ecosystems generally can recover after large-scale pasture disturbances. Onlywhere land has been used too intensively for long periods is reforestation uncertain, butprobably less than 10% of the pasture land in northern Pará has degraded to this level.Nevertheless, the re-growth forest, regardless of pasture-use history, will not necessarily havethe same characteristics of physiognomy or species composition as that originally occupyingthe site. Moreover, as burning becomes more prevalent in eastern Amazonia, abandoned sitesmay not develop into forest and the irreversible degradation of the entire regional ecosystemmust be contemplated.

168

Pyke, D.A. and Archer, S. (1991): Plant-plant interactions affecting plant establishment andpersistence on revegetated rangeland. Journal of Range Management 44:550-557.

Keywords: establishment; rangeland; revegetation; ecosystems; plant-plant interactions;species diversity.


Abstract. Restoration and revegetation of rangeland ecosystems is based on knowledge ofabiotic and biotic interactions that affect plant establishment. Once plants become autotrophic,interactions within and between plant species may occur and these interactions may rangefrom antagonistic to mutualistic. This full range of potential interactions needs to beconsidered to ensure successful revegetation. At the intraspecific level, we propose thedevelopment and use of density-yield diagrams for rangeland species. These diagrams wouldbe based on the self-thinning principle, that aboveground biomass is related to plant densityand to the dynamic process of density-dependent mortality. The proposed approach would beused to determine optimum seeding rates, and to predict future biomass of revegetatedrangelands. At the interspecific level, competitive relationships of species used to reseedrangelands need to be identified to enhance the probability that species will coexist andthereby facilitate greater species diversity on the site. A diversity of species and growth formsmay provide a more stable cover and productivity than a monoculture on sites characterizedby environmental variability while potentially enhancing nutrient status for the site.

169

Mukhammedov, G.M. (1986): Improvement of pastureland in the sand and clay deserts ofthe Central Kara Kum. (In Russian). Problemy Osvoeniya Pustyn 2:11-19.

Keywords: deserts; pastures; sheep; soil chemical properties; soil physical properties;Turkmenistan; shrubs; erosion; desertification; yields; soil salinity; cultivation methods;marginal lands; moisture collection; fertilizers; establishment.

Abstract. The possibilities to create new agrophytocenoses for pasture purposes withoutirrigation or application of fertilizers in the sand and clay deserts of Kara Kum (Turkmenistan)are outlined. Highly productive plant species of different life-forms adapted to the severeecological conditions were selected from native vegetation, woody shrubs and semi-shrubslike black saxaul (Aellenia subaphylla), white saxaul (Haloxylon persicum) and Calligonumsp. being of special importance. In order to improve plant establishment, various agronomictechniques for crust breaking, moisture collection and surface stabilization have to be applied.Newly established plantings must be protected from grazing during the first 5 to 6 years.Improved pasturelands of this type can then help to reduce wind erosion and desertificationproblems as well as improve fodder supply throughout the year and forage yields. (Abstract bybibliography authors)

170

Yadav, I.P.S. and Hazra, C.R. (1989): Research and development linkages for the gainfuluse of wastelands on forage based farm forestry programme. Journal of Rural Development(India) 8:673-680.

Keywords: India; livestock; soil erosion; erosion; agroforestry; trees; shrubs; grasses; legumes;revegetation; marginal lands; acid soil.

Abstract. In India, grazing areas are generally owned by community and are used without anymanagement. Especially marginal and submarginal lands which are usually uneconomical forcrop cultivation are often used for grazing by livestock. Due to very high grazing pressure,these lands devoid of valuable forage species and are continuously subjected to soil erosion.The land utilization patterns are, therefore, being focussed for development of grazingresources on marginal, submarginal and wastelands through adoption of silvi-pastoral and

References 113

agro-forestry systems. Some suitable trees, shrubs, grasses and legumes for salt affected, acid,alkali and other problematic soils of Central India are presented. The success of anydevelopmental programme depends upon the whole-hearted participation of all the agenciesincluding the farmers.

171

Johnson, D.E., Borman, M.M. and Ben Ali, M.N. (1992): Evaluation of plant species forland restoration in central Tunisia. Journal of Arid Environments 22:305-322.

Keywords: revegetation; land restoration; rangeland; introduced species; grasses; legumes;seeds; establishment; yields.

Abstract. Initial screening of 241 plant species, varieties and accessions for potential use inrevegetation was accomplished from 1982 to 1986 throughout Central Tunisia. Plants wererated and ranked on the basis of their survivability, vigor and production. Several promisingplant species were further tested for yield at sites representing the major rangeland types inCentral Tunisia. Several appear to have potential for revegetating rangelands, but on a sitespecific basis. Native species and accessions generally out performed introduced species andaccessions. Annual species were superior to perennial species. The most promising annualgrasses are Lolium rigidum and Bromus mollis. Legumes that have produced well areMedicago truncatula, Hedysarum carnosum and Hedysarum spinosissimum. Perennial grasseshave survived at only two sites and only three species appear to have potential: Oryzopsismiliacea (Syn. Piptatherum miliaceum), Eragrostis curvula and Dactylis glomerata. Theseperennial grasses do not readily establish from seed. Establishment and productivity of allplants were highly variable from year to year and by location.

172

Serrão, E.A.S. (1981): Pasture research results in the Brazilian Amazon. Proceedings of theXIV International Grassland Congress, Lexington (USA), p. 746-750.

Keywords: Amazon region; tropical savanna; tropical forest; Panicum maximum; Brachiariahumidicola; Pueraria phaseoloides; Hyparrhenia rufa; phosphorus; fertilization; pasturemanagement; sustainability; degradation.

Abstract. Natural upland savanna grasslands are represented mainly by well drained savannas,with the cerrado type predominant, and by poorly drained savannas with the campo alto-typebeing the most common. The main limitations are low forage production potential and,especially, low forage quality. About 3 million ha of rain forest has been replaced byimproved pastures of guineagrass (Panicum maximum, 80%), jaraguagrass (Hyparrhenia rufa,10%), and Brachiaria spp. and other grasses (10%). During the first few years afterestablishment, pastures are productive. However, with time, a gradual decline of productivityoccurs, especially in P. maximum pastures. About 0.5 million ha is already in advanced stagesof degradation. Limiting factors include climate and plant and soil factors, besides man'sinfluence. Research was conducted on 14 private ranches representing the most importantimproved- and native-pasture ecosystems of the Amazon region, with the objective ofdeveloping technology for (1) reclaiming sown pastures at varying degrees of degradation, (2)increasing the longevity of still-productive sown pastures in forest areas, and (3) increasingproductivity of low-producing native pastures. Similar trials at all sites include the following:(1) introduction and evaluation of commercial forage species; (2) evaluation of grass-legume


mixtures; (3) forage fertilization; (4) pasture reclamation, improvement and management(grazing trials); and (5) adaptation of new forage germplasm. Results indicate that (1)maintenance of pasture productivity requires careful management of the soil-animal-plantsystem; (2) even though guineagrass has been planted on 2.5 million ha, other grasses can bemore successful; (3) longevity of still-productive guineagrass pastures can be increasedconsiderably by using appropriate grazing-management systems in combination with strategicuse of phosphorus fertilization and legume introduction; (4) reclamation of guineagrasspastures in advanced stages of degradation can be achieved successfully by phosphorusfertilization and by introduction of low-demand grasses such as Brachiaria humidicola incombination with legumes, such as Pueraria phaseoloides.

173

Hall, T.J. (1988): Pasture species are suitable for revegetating degraded granitic soils ofHervey Range military training area in North Queensland. Tropical Grasslands 22:68-72.

Keywords: ground cover; legumes; erosion control; grasses; degradation; revegetation.

Abstract. Twelve pasture species were evaluated for their ability to regenerate eroded shallowgranitic soil supporting a Eucalyptus woodland in the Hervey range military training area,with grazing excluded. Bothriochloa insculpta (Hatch creeping bluegrass) and Melinisminutiflora (molasses grass) were the most successful colonizing grasses; they maintained adense sward for 3 seasons following rough cultivation and fertilization. Bothriochloa pertusa(Indian bluegrass) showed potential to give a low ground cover for camp sites. The legumes,Stylosanthes hamata (Verano) and Macroptilium atropurpureum (Siratro), persisted but theirfoliage covers were too low to control erosion. Hatch creeping bluegrass was the mostpromising grass for erosion control.

174

Howeler, R.H., Sieverding, E. and Saif, S. (1987): Practical aspects of mycorrhizaltechnology in some tropical crops and pastures. Plant and Soil 100:249-283.

Keywords: pastures; cassava; grasses; legumes; beans; soil pH; yields; establishment;fertilization; crop rotation; intercropping; VAM; mycorrhiza; acid soil; phosphorus.

Abstract. Greenhouse and field experiments were conducted on the effect of VA mycorrhiza(VAM) on the growth of cassava, various tropical grass and legume species, as well as beans,coffee and tea. A large number of VAM fungal species were evaluated for effectivity inincreasing cassava growth and P uptake in acid low-P soils. The effectivity of VAM speciesand isolates was highly variable and dependent on soil pH and fertilizer applications, as wellas on soil temperature and humidity. Two species, Glomus manihotis and Entrophosporacolombiana were found to be most effective for a range of crops and pastures, at low pH andat a wide range of N, P and K levels. At very low P levels nearly all crops and pasture specieswere highly mycorrhizal dependent, but at higher soil P levels cassava and several pasturelegumes were more dependent than grass species. Mycorrhizal inoculation significantlyincreased cassava and bean yields in those soils with low or ineffective indigenousmycorrhizal populations. In these soils cassava root yields increased on the average 20-25%by VAM inoculation, both at the experiment station and in farmers' fields. VAM inoculationof various pasture legumes and grasses, in combination with rock phosphate applications,increased their early growth and establishment. Agronomic practices such as fertilization, crop

References 115

rotations, intercropping and pesticide applications were found to affect both the total VAMpopulation as well as its species composition. While there is no doubt about the importance ofVA mycorrhiza in enhancing P uptake and growth of many tropical crops and pastures grownon low-P soils, much more research is required to elucidate the complicated soil-plant-VAMinteractions and to increase yields through improved mycorrhizal efficiency.

175

Osonubi, O., Mulongoy, K., Awotoye, O.O., Atayese, M.O. and Okali, D.U.U. (1991):Effects of ectomycorrhizal and vesicular-arbuscular mycorrhizal fungi on drought tolerance offour leguminous woody seedlings. Plant and Soil 136:131-143.

Keywords: Gliricidia sepium; Leucaena leucocephala; VAM; mycorrhiza; legumes; Albizialebbeck; phosphorus.

Abstract. Seedlings of Acacia auriculiformis A. Cunn. ex Benth., Albizia lebbeck (L.) Benth.,Gliricidia sepium (Jacq.) Walp and Leucaena leucocephala (Lam.) de Wit. were inoculatedwith an ectomycorrhizal (Boletus suillus L. ex Fr.) or indigenous vesicular-arbuscularmycorrhizal (VAM) fungi in a low P soil. The plants were subjected to unstressed (well-watered) and drought-stressed (water-stressed) conditions. In Gliricidia and Leucaena, bothmycorrhizal inoculations stimulated greater plant growth, P and N uptake compared to theirnon-mycorrhizal (NM) plants under both watering regimes. However, in Acacia and Albizia,these parameters were only stimulated by either ectomycorrhiza (Acacia) or VA mycorrhiza(Albizia). Growth reduction occurred as a result of inoculation with other type of mycorrhiza.This was attributed to competition for carbon between Acacia and VA mycorrhizas andparasitic association between Albizia and ectomycorrhiza. Drought-stressed mycorrhizal andNM Leucaena, and drought-stressed mycorrhizal Acacia tolerated lower xylem pressurepotentials and larger water losses than the drought-stressed mycorrhizal and NM Albizia andGliricidia. These latter plants avoided drought by maintaining higher xylem pressurepotentials and leaf relative water content (RWC). All four leguminous plants weremycorrhizal dependent. The higher the mycorrhizal dependency (MD), the lower the droughttolerance expressed in terms of drought response index (DRI). The DRI may be a usefuldeterminant of MD, as they are inversely related.

176

Allen, E.B. (1989): The restoration of disturbed arid landscapes with special reference tomycorrhizal fungi. Journal of Arid Environments 17:279-286.

Keywords: restoration; revegetation; establishment; succession; grasses; mycorrhiza;grassland; plant competition.

Abstract. The loss of mycorrhizal fungi in arid lands through man-caused and naturaldisturbances, including drought, erosion, tillage, and grazing, is a particular problem becausea large proportion of the initial colonizing plant species are non-mycotrophic and theircontinued presence may preclude mycorrhizal establishment. As mycorrhizae are supposed toimprove the growth of several species which are useful for land restoration and to increasetheir ability to compete with colonizing non-mycotrophic annuals, it was tested if the additionof mycorrhizal inoculum and removal of non-mycotrophic annuals would increase the rate ofmycotrophic plant establishment and succession on disturbed sites in SW Wyoming. Afterthree years of growing surprising results were obtained: (1) On high-nutrient soils coupled


with relatively high precipitations, mycorrhizae may act as a carbon drain, thereby decreasingthe growth of planted grass (Agropyron species). (2) On poor soils where wind was animportant factor, non-mycotrophic annuals were facilitating grass establishment, rather thancompeting with the grasses. (3) In soils of high inoculum, mycorrhizal fungi seemed to exertsome kind of 'pathogenic' effect on non-mycotrophic species by directly reducing their growthand density. Thus, a high initial density of mycorrhizal inoculum may either hinder or promotethe early stages of succession and an understanding of the heterogeneity of the landscape iscritical before making decisions such as whether to inoculate, or whether to rely on naturaldispersal of mycorrhizal fungi. (Abstract by bibliography authors)

177

Archer, S. and Pyke, D.A. (1991): Plant-animal interactions affecting plant establishmentand persistence on revegetated rangeland. Journal of Range Management 44:558-565.

Keywords: establishment; rangeland; ecosystems; seeds; revegetation; mycorrhiza;invertebrates; rhizobia; succession; pollination; animal-plant interaction.

Abstract. The role of ungulate grazing in shaping rangeland ecosystems is well known relativeto other important plant-animal interactions such as pollination, seed dispersal, granivory, andbelowground herbivory. Successful rangeland revegetation may be enhanced by strategies thatfavor certain groups of animals and discourage others. Many perennial forbs and shrubsrequire animals for successful pollination, reproduction, and subsequent maintenance ofspecies on a site; however, pollination biology of many rangeland plants and pollinatorabundances at potential revegetation sites are largely unknown. Granivory may be significantin some locations and planning and design of revegetation areas may be improved byimplementing principles of seed escape mechanisms, such as predator satiation, seed escape inspace (low perimeter-to-area ratio for revegetation site), and seed escape in time (synchronousor staggered timing for nearby revegetation sites). Seedling establishment may be associatedwith invertebrate population levels which need to be considered in future revegetationprojects. Timing and site preparation are important in limiting belowground herbivory.Animals can serve as dispersal agents of seeds. Livestock dosed with desirable seeds candisperse them in their dung across the landscape, thereby creating patches of desirable plants.If revegetation sites will be grazed by livestock, then managers should choose plant speciesthat tolerate rather than avoid grazing and should apply adequate management to establish andmaintain plant populations. Seed inoculated with mutualistic species such as mycorrhizae,nitrogen-fixing bacteria, or actinomycetes may enhance establishemnt, productivity, andnutrient quality of rangeland species while increasing rates of succession.

178

Sundararaju, R. and Chinnathurai, A.K. (1992): Technology packages for reclamation anddevelopment of wastelands. Indian Forester 118:609-615.

Keywords: reforestation; Cassia siamea; Eucalyptus; reclamation.

Abstract. In wasteland afforestations utmost care should be taken for selection of properspecies. In areas of poor depth of soil and poor moisture retention application of fertilizers andtank silt/organic manure will increase success. Wrightia tinctoria, Hardwickia binata, Albiziaamara will suit well. In social forestry, failure in plantation can be brought down by soiltesting and selecting suitable species with some reclamation measures. Experiments in Tamil

References 117

Nadu indicate that Casuarina performs well in mine spoils. Acacia planifrons, Acaciamellifera and Casuarina junghuhniana could be used in drought prone area. Area undersevere saline/alkaline problems could be improved by applying gypsum and fertilizers withdrainage facilities. Cassia siamea, Casuarina, Eucalyptus camaldulensis and Azadirachtaindica grow well even in such area.

179

Bellotti, W.D., Bowman, A. and Silcock, R.G. (1991): Sustaining multiple productionsystems. 5. Sown pastures for marginal cropping lands in the subtropics. Tropical Grasslands25:197-204.

Keywords: pastures; subtropics; Australia; mixed farming; sustainability; semiarid zones;grasses; legumes; mulch; ley farming.

Abstract. Fertility and structure of surface soil is declining throughout the marginal drylandcroplands of eastern Australia. The incorporation of a pasture phase in the cropping sequenceappears to be the most promising option for developing a sustainable cropping system.However, special problems currently restrict the use of sown pastures in these lands insubtropical Queensland and NSW. For much of the region, productive and persistent pasturespecies have been identified. These include the native grasses, Astrebla lappacea andDichanthium sericeum. Perennial grasses are still needed on the lighter textured infertile soilsand there are still no adapted summer growing legumes for frost prone areas. Unreliableestablishment is currently the main technical constraint limiting wider use of the availablepasture species. Strategies for overcoming this constraint are discussed and include decisionsupport packages using climatic and biological models, improving establishment by means ofaerial seeding, mulches and stubbles, and management for improving the supply of soilmoisture.

180

Plowright, R.C. and Hartling, L.K. (1981): Red clover pollination by bumble bees: A studyof the dynamics of a plant-pollinator relationship. Journal of Applied Ecology 18:639-647.

Keywords: insect pollination; bumble bees; Trifolium pratense.

Abstract. (1) A 3-parameter probabilistic model provided a good fit to data relating seed set tothe number of florets visited on red clover inflorescences by bumble bees. (2) The model,incorporated as a component in a computer simulation of bees foraging on a patch of redclover plants, was used to compare the pollinating efficiency of bees with differentbehavioural specifications with respect to the number of florets they visit per inflorescence.(3) Insects which visited only a few florets on each inflorescence were found almost always tocause lower seed set than those which based their decision to leave on the reward status of theinflorescence, even though the rate of inter-inflorescence transitions was greater for the formerbehavioural specification. Since the second type of behaviour is characteristic of real bumblebees and always returns higher profit to the insect, it is concluded that the coevolutionaryrelationship between Bombus and red clover is adapted to maximize the self interest of bothpartners.


181

Ahmad, A. (1992): Environmental degradation and possible solutions for restoring the land:A case study of magnesite mining in the Indian Central Himalayas. Desertification Bulletin(UNEP) 21:15-23.

Keywords: degradation; India; ecosystems; mining; regeneration; revegetation; soil erosion;grasses.

Abstract. In India, the total land area under mining is estimated at about 7,854 km2. In 1982,there were about 4,052 working mines, excluding those producing oil, gas, atomic energy,minerals and minor minerals. Of these, 2,854 were mining non-metallic minerals, 720 weremining metallic minerals and the remaining 478 were mining coal and lignite. Among thenon-metallic minerals, magnesite mining plays an important role because of its major use inIndia's steel industry. Mining must be one of the most destructive of all of man's activities onthe environment. It destroys the original ecosystem and replaces it with only an empty pit, asterile wasteland, or both. Consequently, mined land represents a fascinating challenge toscientists who are attempting to find ways of restoring the original ecosystem. This presentstudy was undertaken to rehabilitate a damaged, mined ecosystem using an ecologicalapproach for sustainable development. (Abstract by bibliography authors)

182

West, N.E. (1993): Biodiversity of rangelands. Journal of Range Management 46:2-13.

Keywords: rangeland; genetics; ecosystems; invertebrates; livestock; biodiversity; speciesdiversity; sustainability.

Abstract. Biodiversity is a multifaceted phenomenon involving the variety of organismspresent, the genetic differences among them, and the communities, ecosystems, and landscapepatterns in which they occur. Society will increasingly value biodiversity and influence thepassage of laws and writing of regulations involving biodiversity which rangeland managerswill have to abide by over the coming decades. While taxonomic knowledge of vertebratesand vascular plants and their abundance, rarity, and distribution, in the developed nations isgenerally adequate, the same cannot be said of the developing world. Furthermore, adequateknowledge of invertebrates, nonvascular plants, and microbes is deficient everywhere.Although the basis of variation at all higher levels, genetic variation within rangeland species,even the major ones, has barely been assessed. Obtaining statistically adequate data onpopulations of rare species that are small and secretive is well nigh impossible. We have manymeans of measuring community diversity, but all of them are value laden. That is, choice ofvariables to measure and how they are indexed betrays what we consider are important. Weshould be more forthright in stating to the users the biases of these methods. There are manyother, more useful ways to describe community-level diversity besides the traditional focus onspecies. Ungulate grazing is an important process in many ecosystems. Thus, removal ofgrazing destabilizes some systems. Livestock grazing will actually increase the chances ofsurvival of some species. Moderate livestock grazing can also enhance community andlandscape-level diversity in many instances. Attention is now shifting from "charismatic"species to defensively managing larger tracts of land with habitat or ecosystems holding suitesof sensitive species. Since some accelerated extinction of isolated populations and species isinevitable, we need to know which species and ecotypes are most valuable. Understanding ofmodular, guild, and functional group structure would also help us identify keystone or criticallink species and better focus our attention on truly important tracts of land where they live. It

References 119

is probably more important to sustain soils and ecosystem processes than any randomlyselected species, especially if functionally redundant species can be identified. Similarly, notall introduced, alien, or exotic species are equal threats; it depends on how they fit intoecosystems. Sustainable development will depend on finding balance between use andprotection, from range sites to landscapes, and even on a global basis.

183

Miranda, E.E.de and Mattos, C. (1992): Brazilian rain forest colonisation and biodiversity.Agriculture, Ecosystems and Environment 40:275-296.

Keywords: biodiversity; ecosystems; deforestation; economics; tropical forest; speciesdiversity; degradation; Brazil; Amazon region.

Abstract. This work explains the tropical rain forest's main characteristics, and the reasonswhy this ecosystem plays an important role in determining global biodiversity. The occupationprocess of the two Brazilian tropical rain forests (Atlantic and Amazon) are briefly described,with quantitative information on deforestation and its consequences. Human presence in theseareas is millenary, and its role as a source of increase, decrease and maintenance ofbiodiversity are exemplified. Different kinds of man/forest interactions (such as thosecharacterizing indigenous people, riverside communities, caboclos, rubber tappers andagriculturists) and their relation to biodiversity, are described. The future occupation of theBrazilian tropical rain forest supplanting past mistakes, especially in the Amazon, is proposedas a triple challenge. The first challenge is to stop the destruction of the still-intact forest, andto plan its rational occupation. An example of how this has been done by rubber tappers in thestate of Acre, and how it affects wildlife and vegetation communities is given. The secondchallenge is to reduce the migration flow towards the economic frontier areas, and to proposeto the thousands of agriculturists already installed there alternatives to reconcile economicdevelopment and environmental preservation. In this case, the situation of a colonizationproject in the state of Rondônia is described. The third challenge is to restore the biodiversityin the almost 400 000 km2 of land that have been occupied and degraded for a long time, as inthe state of Tocantins. An example of how scientific research contributes to meeting thischallenge is described.

184

Pimm, S.L. and Gittleman, J.L. (1992): Biological diversity: Where is it? Science 255:940.

Keywords: biodiversity; tropics; species diversity.

Abstract. Some knowledge gaps and facts concerning the distribution of species across theplanet (e.g., temperate and tropical diversity), their number in a specific habitat, and theturnover of species across space are discussed in this short paper. (Abstract by bibliographyauthors)

185

Huston, M. (1979): A general hypothesis of species diversity. American Naturalist 113:81-101.

Keywords: species diversity; models; ecosystems; biodiversity.


Abstract. A new hypothesis, based on differences in the rates at which populations ofcompeting species approach competitive equilibrium (reduction or exclusion of some species),is proposed to explain patterns of species diversity. The hypothesis assumes that mostcommunities exist in a state of nonequilibrium where competitive equilibrium is prevented byperiodic population reductions and environmental fluctuations. When competitive equilibriumis prevented, a dynamic balance may be established between the rate of competitivedisplacement and the frequency of population reduction, which results in a stable level ofdiversity. Under conditions of infrequent reductions, an increase in the population growthrates of competitors generally results in decreased diversity. This model clarifies anunderlying pattern of variation in diversity and points out the common elements of previoushypotheses. Rather than arguing that either competition, predation, or productivity controldiversity, it demonstrates that all of these may contribute to the same basic mechanism. Indoing so, it not only explains the correlations of the other hypotheses with patterns ofdiversity, but also explains the exceptions that these hypotheses could not explain. Thishypothesis may be applied to variations of diversity both on a latitudinal gradient and withinspecific regions.

186

Walker, B.H. (1992): Biodiversity and ecological redundancy. Conservation Biology 6:18-23.

Keywords: biodiversity; species diversity; ecosystems.

Abstract. This paper addresses the problem of which biota to choose to best satisfy theconservation goals for a particular region in the face of inadequate resources. Biodiversity istaken to be the integration of biological variability across all scales, from the genetic, throughspecies and ecosystems, to landscapes. Conserving biodiversity is a daunting task, and thepaper asserts that focusing on species is not the best approach. The best way to minimizespecies loss is to maintain the integrity of ecosystem function. The important questionstherefore concern the kinds of biodiversity that are significant to ecosystem functioning. Tobest focus our efforts we need to establish how much (or how little) redundancy there is in thebiological composition of ecosystems. An approach is suggested, based on the use offunctional groups of organisms defined according to ecosystem processes. Functional groupswith little or no redundancy warrant priority conservation effort. Complementary species-based approaches for maximizing the inclusion of biodiversity within a set of conservationareas are compared to the functional-group approach.

187

McNaughton, S.J. (1993): Biodiversity and function of grazing ecosystems. In: Schulze, E.D.and Mooney, H.A. (eds.), Biodiversity and Ecosystem Function. Berlin: Springer-Verlag, p.361-383.

Keywords: biodiversity; grazing; ecosystems; grassland; species diversity; USA; savanna;Tanzania; California.

Abstract. Fundamental ideas about biodiversity and function of grazing ecosystems areamplified throughout this report. The author looks at the general nature of diversity ingrasslands and the relationships between productivity, stability and species diversity. Data arepresented from studies of (a) abandoned agricultural fields in Central New York State, USA,(b) the savanna grasslands of Serengeti National Park, Tanzania, and (c) the grasslands of

References 121

Yellowstone National Park, USA. There is evidence that primary productivity, as measured bythe change in total community standing crop, is inversely related to diversity. Thesuccessional studies, however, indicated that species’ productivities are spaced more evenlythrough the growing season in more diverse vegetation. (Abstract by bibliography authors)

188

Ehrlich, P.R. and Wilson, E.O. (1991): Biodiversity studies: Science and policy. Science253:758-762.

Keywords: biodiversity; economics; ecosystems; deforestation; tropical forest.

Abstract. Biodiversity studies comprise the systematic examination of the full array ofdifferent kinds of organisms together with the technology by which the diversity can bemaintained and used for benefit of humanity. Current basic research at the species levelfocuses on the process of species formation, the standing levels of species numbers in varioushigher taxonomic categories, and the phenomena of hyperdiversity and extinction proneness.The major practical concern is the massive extinction rate now caused by human activity,which threatens losses in the esthetic quality of the world, in economic opportunity, and invital ecosystem services.

189

Burton, P.J., Balisky, A.C., Coward, L.P., Cumming, S.G. and Kneeshaw, D.D. (1992):The value of managing for biodiversity. The Forestry Chronicle 68:225-237.

Keywords: biodiversity; ecosystems; sustainability; genetics; species diversity; silvopastoralsystems.

Abstract. The concept of biological diversity (biodiversity) is reviewed, with special attentionto its measurement and natural trends. While generalizations regarding the necessity ofbiodiversity need to be interpreted with caution, it is argued that biodiversity should beprotected in more ecosystem and landscape reserves, and that biodiversity is a reasonablemanagement objective on timber lands as well. Maintaining biodiversity is important becausewe cannot always identify which individual species are critical to ecosystem sustainability, norwhich species may be useful to mankind in future. Many wild species can provide usefulnatural products and genetic material, and can serve as ecological indicators. Diversity reducespest and disease problems, and encourages recovery from disturbance. Uncertainty exists withregard to climate change and future socioeconomic values. It is therefore prudent to maximizeflexibility by promoting a wide array of species and potential products. Suggestions areoffered on how to promote biodiversity in multiple-use forests.

190

Chalmers, N. (1992): Saving the ark. Science and Public Affairs London 7(4):14-19.

Keywords: biodiversity; deforestation; ecosystems; sustainability; species diversity.

Abstract. Biodiversity is being lost due to deforestation, draining of wetlands and release oftoxic waste, amongst other activities. It is estimated that a quarter of the world's biodiversitymay be under serious threat of extinction over the next 20-30 years (15 000 to 50 000species/year). Three long-term benefits of biodiversity conservation, namely, socioeconomic,


ecosystem service and cultural are described. The importance of scientists in the study of theworld's biodiversity, provision of politicians with priorities for conservation, monitoring theeffects of sustainable use of biodiversity and education of the public on the importance ofbiodiversity are discussed using examples of work currently being undertaken by the NaturalHistory Museum in collaboration with other institutes.

191

Clement, J. (1991): Que penser de la déforestation des pays tropicaux? ONF - BulletinTechnique 21:259-267.

Keywords: deforestation; genetics; biodiversity; tropical forest.

Abstract. Deforestation in tropical countries has dramatically accelerated during the lastdecade, jumping from some 11 million hectares per year to nearly 20 million. This primarilyaffects the local populations, who are deprived of essential commodities provided by forestssuch as fuelwood, fruits, medicines, game, etc., as well as the economics of tropical countries,whose timber resources go up in smoke, and deforested soils are inexorably degraded.Moreover, international public opinions are concerned about impact of forest destruction onglobal climatic equilibria and the preservation of genetic biodiversity. Remedies fordeforestation lie for the most part outside the forest sector: food and energy security,harmonious land-use management, etc. On the other hand, the Tropical Forest Action Planlaunched in 1985 has as an objective to promote development of new policies aimed atrestoring equilibrium between man and his environment within the framework of a sustainableutilization of natural resources.

192

Lugo, A.E., Parrotta, J.A. and Brown, S. (1993): Loss in species caused by tropicaldeforestation and their recovery through management. Ambio 22:106-109.

Keywords: deforestation; degradation; tropical forest; models; trees; biodiversity; speciesdiversity.

Abstract. The loss of species as a result of deforestation and degradation of tropical forestlands is widely discussed. Models based on island biogeography theory are used to evaluatethe relationship between extinctions of species and deforestation. The analysis shows thatnatural resiliency causes the models to overestimate the rates of species extinctions for givenintensities of deforestation. There is an opportunity to couple natural processes withmanagement activities to reduce species extinctions and restore species richness to degradedlands. As an example we show how tropical monoculture tree plantations can foster diversenative forests in areas previously deforested. The central point is that well-directed humanactions provide us with the means to conserve biodiversity and restore it in locationspreviously degraded.

193

Murgueitio, E. (1990): Intensive sustainable livestock production: An alternative to tropicaldeforestation. Ambio 19:397-400.

References 123

Keywords: deforestation; sustainability; tropical forest; Colombia; forage trees; sugarcane;sheep; yields; swine; pastures; degradation.

Abstract. To solve the problem of tropical forest destruction demands a strategy which is ofnecessity complex, and yet must also be aggressive, if the remaining tropical forest areas withtheir ecological riches and biological diversity are to be preserved. Intensive livestockproduction models, based on true tropical resources, appear to offer real alternatives to thepressures exerted by the major enemy of the forest - the extensively grazed beef animal. Themodel developed in Colombia employs perennial crops with high biomass productionpotential (sugarcane and forage trees) and complementary livestock species (pigs and sheep)managed in confinement. Productivity is a function of sugarcane yield which depends on soilfertility, water availability and variety. For the world average yield of 50 t/ha per year, totalliveweight production per year from pigs and sheep can be 1500 kg/ha per year. However,with appropriate management, sugarcane can yield up to 180 t/ha per year, which will give8000 kg liveweight pr hectare per year. Implementing these models on a massive scale willresult in a substantial reduction of the area required to support resource-poor farmers,committed to colonizing the forest. At the same time, existing grazing areas can betransformed into more productive units with obvious advantages in terms of job creation andeconomic stimulus to rural development. More research and development is needed, andespecially the validation of the technologies in areas where the rate of forest destruction ismost acute.

194

Westoby, M., Walker, B. and Noy-Meir, I. (1989): Opportunistic management forrangelands not at equilibrium. Journal of Range Management 42:266-274.

Keywords: rangeland; animal-plant interaction; grassland; livestock; pasture management;succession; models.

Abstract. We discuss what concepts or models should be used to organize research andmanagement on rangelands. The traditional range succession model is associated with themanagement objective of achieving an equilibrium condition under an equilibrium grazingpolicy. In contrast, the state-and-transition model would describe rangelands by means ofcatalogues of alternative states and catalogues of possible transitions between states.Transitions often require a combination of climatic circumstances and management action(e.g., fire, grazing, or removal of grazing) to bring them about. The catalogue of transitionswould describe these combinations as fully as possible. Circumstances which allow favorabletransitions represent opportunities. Circumstances which threaten unfavorable transitionsrepresent hazards. Under the state-and-transition model, range management would not seeitself as establishing a permanent equilibrium. Rather, it would see itself as engaged in acontinuing game, the object of which is to seize opportunities and to evade hazards, so far aspossible. The emphasis would be on timing and flexibility rather than on establishing a fixedpolicy. Research under the state-and-transition model would aim to improve the catalogues.Frequencies of relevant climatic circumstances would be estimated. Hypotheses abouttransitions would be tested experimentally. Often such experiments would need to be plannedso that they could be implemented at short notice, at an unknown future time when therelevant circumstances arise.


195

McIvor, J.G. and Orr, D.M. (1991): Sustaining productive pastures in the tropics. 2.Managing native grasslands. Tropical Grasslands 25:91-97.

Keywords: pastures; tropics; grassland; natural pastures; Australia; sustainability; animalproduction.

Abstract. The grasslands of tropical Australia include the naturally treeless, grass dominatedcommunities and the grassy understories of the widespread woodlands and shrublands.Information from the monsoon tallgrass, tropical and subtropical tallgrass, tussock grasslands(Mitchell grass) and Acacia (mulga) shrublands is used to show how management caninfluence grassland performance. Emphasis is placed on vegetation responses but effects onsoil characteristics and animal production are also considered. The major management optionsconsidered are control of stock (numbers, species, breeds, when and where they graze), fire,feed supplements and timber treatment. Changes in land condition in the Burdekin catchmentin response to management and seasonal conditions are outlined. The various options must beintegrated and the role of decision support packages is considered. Major changes areoccurring in the northern grasslands and future management research should include studies ofthe ecology of the main grass species, the biology and management of woody plants, otherpasture types (e.g., Bothriochloa/Aristida lands), stocking rate/animal productionrelationships, the costs and benefits of management practices, e.g. temporary overgrazing, andgrazing systems for changing pasture composition and animal production.

196

Belsky, A.J. (1986): Does herbivory benefit plants? A review of the evidence. AmericanNaturalist 127:870-892.

Keywords: grazing; animal-plant interaction; evolution; herbivory.

Abstract. The potential benefits of herbivory to plants have been debated over the last decade.Several investigators claim that removal of or damage to the productive, absorptive, orreproductive tissue of plants by herbivores benefits some plant species by increasing their netprimary productivity, seed production, or longevity, and that these changes increase plantfitness and result in the evolution of herbivore-plant mutualisms. Although more than 40papers have been cited as presenting experimental evidence in support of these benefits andmutualisms, strong evidence is lacking. Increased plant biomass as a result of tissue removalhas been found only under growth-chamber conditions and in cultivated crops. Althoughherbivores may benefit certain plants by reducing competition or removing senescent tissue,no convincing evidence supports the theory that herbivory benefits grazed plants.

197

Eng, P.K., Kerridge, P.C. and Mannetje, L.'t (1978): Effects of phosphorus and stockingrate on pasture and animal production from a guinea grass-legume pasture in Johore,Malaysia. 1. Dry matter yields, botanical and chemical composition. Tropical Grasslands12:188-197.

Keywords: phosphorus; stocking rate; pastures; animal production; grass-legume pastures;yields; chemical composition; grasses; nitrogen; succession; species diversity.

References 125

Abstract. Changes in yield on offer, botanical composition, species frequency and chemicalcomposition were measured from a continuously grazed guinea grass-legume (stylo, centro,puero) pasture over three years. The treatments were a factorial combination of three stockingrates and four annual maintenance rates of phosphorus comprising three rates of rockphosphate and one of superphosphate. Pasture availability remained relatively constant at thelow stocking rate, after the first year at the medium stocking rate, but declined markedly overthe three years at the high stocking rate. The proportion of guinea grass, which was dominant,decreased with stocking rate in the third year. That of centro and stylo increased after the firstyear and was not affected by stocking rate except that of centro at the high stocking rate in inthe third year. Puero disappeared from the pasture at all stocking rates after two years. Thephosphorus treatments had no effect on presentation yields. There was a significant increase inphosphorus concentration of all species and calcium concentration of guinea grass withincreasing rates of rock phosphate during the second and third year. Phosphorus treatmentshad no effect on the nitrogen concentration of species except for stylo in the third year.

198

Ryder, R.A. (1980): Effects of grazing on bird habitats. In: DeGraff, R.M. and Tilghmann,N.G. (eds.), Management of Western forests and grasslands for nongame birds. Ogden: USForest Service, Gen. Tech. Rep. INT-86 Intermount. Res. Sta., p. 51-66.

Keywords: grazing; grassland; livestock; rodents; birds; grasses; biodiversity; insects; speciesdiversity.

Abstract. Feeding on plants by various herbivores, especially livestock and big game but alsoby rodents, lagomorphs, insects and even some birds and reptiles, can alter vegetativecommunities as habitat for birds. Species composition of plants, density of stands, vigor, seedand insect production, and growth form of plants often change due to grazing. Removal ofvegetative cover as well as trampling may expose soils to increased wind and water erosion.In shortgrass, for example, resultant gullies may provide new nesting habitat for rock wrens,rough-winged swallows, Say's phoebes, and barn owls while reducing nesting, escape andyoung-rearing habitat for species requiring denser stands of taller grasses such asmeadowlarks and lark buntings. Just as some plants such as buffalo grass and blue grama canbe considered "increasers" with grazing of shortgrass prairie so can horned larks, McCown'slongspurs, and mountain plovers. Likewise, western meadowlarks, lark buntings and Brewer'ssparrows tend to be "decreasers" similar in response to that of western wheatgrass, needle-and-thread and fourwing saltbush to increased summer grazing by cattle on shortgrass rangesin northcentral Colorado. Differences in effects of grazing on vegetation and soils by variousclasses of livestock, species of big game, different levels of intensity and seasons of use willbe discussed with stress on examples from western forest and grassland types.

199

Paige, K.N. and Whitham, T.G. (1987): Overcompensation in response to mammalianherbivory: The advantage of being eaten. American Naturalist 129:407-416.

Keywords: animal-plant interaction; seed production.

Abstract. Plants of scarlet gilia, Ipomopsis aggregata, are exposed to high levels ofmammalian herbivory (by mule deer, Odocoileus hemionus, and elk, Cervus elaphus) early inthe season, before flowering. During this period of our study, up to 56% of all individuals


experienced a 95% reduction in aboveground biomass. Browsed plants rapidly responded byproducing new inflorescences and flowering within 3 wk. Unbrowsed plants produced onlysingle inflorescences, whereas browsed plants produced multiple inflorescences. Fieldobservations and experimental manipulations showed that plants with multiple inflorescencesproduced significantly greater numbers of flowers and fruits than unbrowsed individuals.Because there were no differences between browsed an unbrowsed individuals in the numberof seeds produced per fruit, seed weight, subsequent germination success, and survival,browsed plants enjoyed a 2.4-fold increase in relative fitness. Consequently, there is animmediate reproductive advantage to being eaten. Under the natural field conditions of thisstudy, mammalian herbivores played a beneficial role in the survival and reproductive successof scarlet gilia.

200

Waser, N.M. and Price, M.V. (1981): Effects of grazing on diversity of annual plants in theSonoran desert. Oecologia 50:407-411.

Keywords: deserts; species diversity; cattle; models; animal-plant interaction.

Abstract. A two-year survey of winter-germinating annual plants in southern Arizonaindicates that species diversity declines consistently as a function of increasingly recentgrazing by cattle. This finding conflicts with reports that predators enhance prey speciesdiversity in some marine and terrestrial systems. Consideration of equilibrium andnonequilibrium models suggests, however, that enhanced diversity should occur only foropen, multi-celled prey populations experiencing intermittant predation. These generalconditions appear not to hold for the cattle-annual plant system.

201

Caldwell, M.M., Richards, J.H., Johnson, D.A., Nowak, R.S. and Dzurec, R.S. (1981):Coping with herbivory: Photosynthetic capacity and resource allocation in two semiaridAgropyron bunchgrasses. Oecologia 50:14-24.

Keywords: grasses; animal-plant interaction.

Abstract. Agropyron desertorum, a grazing-tolerant bunchgrass introduced to the western U.S.from Eurasia, and Agropyron spicatum, a grazing-sensitive bunchgrass native to NorthAmerica, were examined in the field for photosynthetic capacity, growth, resource allocation,and tiller dynamics. These observations allowed identification of physiological characteristicsthat may contribute to grazing tolerance in semiarid environments. Following defoliation, A.desertorum plants rapidly reestablished a canopy with 3 to 5 times the photosynthetic surfaceof A. spicatum plants. This difference was primarily due to the greater number of quicklygrowing new tillers produced following defoliation. Agropyron spicatum produced few newtillers following defoliation despite adequate moisture, and carbohydrate pools that wereequivalent to those in A. desertorum. Leaf blades of regrowing tillers had higherphotosynthetic capacity than blades of unclipped plants of both species, but the relativeincrease, considered on a unit mass, area, or nitrogen basis, was greater for A. desertorum thanfor A. spicatum. Agropyron desertorum also had lower investment of nitrogen and biomassper unit area of photosynthetic tissues, more tillers and leaves per bunch, and shorter livedstems, all of which can contribute to greater tolerance of partial defoliation.

References 127

202

Owen, D.F. (1980): How plants may benefit from the animals that eat them. Oikos 35:230-235.

Keywords: grasses; animal-plant interaction; insect-plant interaction; nutrient cycle; nitrogenfixation.

Abstract. It is suggested that the mutually beneficial relationships between flowers and theirpollinators and between fruits and fruit-eaters can be extended to cover a much wider range ofplant-consumer interactions. The ability to photosynthesize is by itself of limited value to aplant if growth and reproduction are restricted by the availability of nutrients. Hence naturalselection should favour adaptations that increase the rate of supply of a scarce resource. Byenlisting the "help" of a consumer a plant may facilitate cycling and increase the supply of anutrient in short supply; in particular the deposition of sugary honeydew by aphids mayincrease the rate of nitrogen fixation beneath the plant by providing an energy source to free-living nitrogen-fixing bacteria. Consumers may also affect the growth form of a plant in abeneficial way; grasses, for example, survive best when cropped and are probably totally co-evolved with grazers: one would not be possible without the other. A speculative paper as thisalmost certainly contains errors of interpretation, but even if only some of the suggestions arecorrect the common viewpoint that plants defend themselves against consumers will have tobe radically changed.

203

Maschinsky, J. and Whitham, T.G. (1989): The continuum of plant responses to herbivory:The influence of plant association, nutrient availability, and timing. American Naturalist134:1-19.

Keywords: animal-plant interaction.

Abstract. In a single population of Ipomopsis arizonica (Polemoniaceae), we show acontinuum of compensatory responses to vertebrate herbivory. We demonstrateexperimentally that the degree of herbivore impact depends on plant association, nutrientavailability, and timing of grazing. From 1985 to 1987, the most common response tovertebrate herbivory was equal compensation, whereby grazed plants set numbers of fruit andseeds equal to controls within the same growing season. However, we also observed cases ofsignificant overcompensation and undercompensation. In 1985 and 1987, overcompensationoccurred in vertebrate-grazed plants that were supplemented with nutrients and growing freeof competition. These plants produced 33% to 120% more fruit than control, ungrazed plants.Cases of undercompensation occurred in groups where I. arizonica grew in association withgrasses or where nutrients were not supplemented. Grazed and clipped plants in these groupsproduced from 28% to 82% as many fruits as did ungrazed controls. Our studies indicate thatthe compensatory response of plants to grazing is probabilistic when three external factors areconsidered. The probability of compensation for herbivory decreases as competition withother plants increases, as nutrient levels decrease, and as the time of herbivory comes later inthe growing season.


204

Milchunas, D.G., Sala, O.E. and Lauenroth, W.K. (1988): A generalized model of theeffects of grazing by large herbivores on grassland community structure. American Naturalist132:87-106.

Keywords: models; grassland; animal-plant interaction; plant competition; plant succession;succession; evolution.

Abstract. Current disturbance models do not adequately account for the wide range ofresponses by grassland plant communities to grazing by large generalist herbivores. Theevolutionary history of grazing, an important factor in the response of grasslands to grazing,has not been explicitly addressed. Grazing history alone, however, is not a good predictor ofplant-herbivore interactions. Interactions occur along gradients of convergent to divergentselection pressures with increasing environmental moisture and of intolerance to tolerance ofgrazing with increasingly long evolutionary histories of grazing. We suggest that feedbackmechanisms between plants and grazing animals are well developed in grasslands with longevolutionary histories of grazing. Feedback mechanisms are manifest in the rapid switchingcapabilities (of plant species and modes of competition) of subhumid grasslands with longevolutionary histories of grazing and divergent selection pressures. Switching capabilities donot exist in semiarid grasslands with long evolutionary histories of grazing and convergentselection pressures. Rather, for heavily grazed dominant species dominance increases.Feedback mechanisms are not well developed in systems with short evolutionary histories ofgrazing. In these cases, the differences in response to grazing by semiarid and subhumidsituations arise primarily from differences in the grazing tolerance of plants adapted tosemiaridity or of plants adapted to competition for light and from the different effects ofgrazing on canopy structure.

205

Walker, B. (1991): Sustaining tropical pastures - summative address. Tropical Grasslands25:219-223.

Keywords: natural pastures; animal production; sustainability; Australia; farming systems;pastures; weeds.

Abstract. By the year 2000 over 95% of the pastoral areas of northern Australia will stillconsist of native pastures. Previous studies show that in Queensland, about 50-60% of nativepastures are in good condition; 30% require low key-management inputs to improve them andthe remainder will need a major capital outlay to restore them. Research inputs into nativepastures fall well below those required. In addition to current work described at thisconference, an assessment of the present condition and health of the grazing lands, togetherwith an ongoing program to monitor trends, particularly in high risk areas, is urgently needed.Management packages directed at specific needs for local areas are required. An optimisticscenario for development of introduced pasture over the next decade is that sown andnaturalized pastures will increase from the present 9.8 to 13.4 m ha. Areas of fodder crops willincrease from 500 000 to 1.0 m ha and clearing of woodlands and control of woody weedswill continue at least at the present level of 500 000 ha per year. Most of this developmentwill be on the more fertile soils in the above 600 mm mean annual rainfall areas south ofTownsville. Research emphasis should now move away from species development todeveloping management systems for optimal productivity and stability. Scientists and advisorshave not been successful in developing sound guidelines on the development and management

References 129

of pastoral systems sustainable on a whole property basis up to the present time. Producers aremore advanced in their thoughts and actions on sustainable systems and their knowledge andexperience should be accessed before any new work is undertaken. An over riding influenceon long term work on sustainable pastoral systems is the shortage of funds and resources.Administrators and research leaders will need to make some tough decisions on researchpriorities.

206

Lonsdale, W.M. (1994): Inviting trouble: Introduced pasture species in northern Australia.Australian Journal of Ecology 19:345-354.

Keywords: pastures; Australia; weeds; grasses; legumes; seeds; introduced species.

Abstract. I surveyed the history of exotic pasture introductions in northern Australia tocompare the rate of introduction of useful species with that of weeds. Between 1947 and 1985,463 exotic grasses and legumes in at least 2033 accessions were intentionally introduced intothe region, the grasses predominantly from Africa, and the legumes from Central and SouthAmerica. Of these, only 21 (5%) came to be recommended as useful, while 60 (13%) becamelisted as weeds. Seventeen of the useful plants were in fact also weeds, leaving only 4 species(<1%) that were useful without causing weed problems. They were far outnumbered by the 43species (9%) that were weeds but had no recorded use. Of the 60 weeds, 21 were weeds ofcropping, 20 were weeds of conservation and 19 were weeds of both sectors. Thirteen werelisted as major crop weeds. Growth rate, maximum height, seed size, and continent of originwere unrelated to weediness. Good predictors of weediness were whether a plant was useful, agood performer in trials, or persisted at a field site. In addition, grasses were more likely, andlegumes less likely, to be weedy than expected. It is argued that a new form of assessment isrequired before an exotic plant species is released into Australian environment as a pastureplant. This would recognize that a successful introduction is almost certain to become a weedin some situations, and would attempt to assesss the net national benefit of the proposedintroduction.

207

Johnson, H.B. and Mayeux, H.S. (1992): Viewpoint: A view on species additions anddeletions and the balance of nature. Journal of Range Management 45:322-333.

Keywords: ecosystems; deserts; establishment; tropics; species diversity; rangeland;vegetation change; introduced species; evolution.

Abstract. Popular assumptions about ecosystem stability and the delicate balance of nature arefound lacking when examined in terms of paleoecological, historical and currentbiochronological, and biogeographical sequences in a wide variety of environments. Speciescomposition of vegetation varies continuously in time as well as space in the absence of acuteperturbations. Species have been added or removed from ecosystems without greatly affectingecosystem function. Natural ecosystems exhibit greater stability (inertia) in physiognomicstructure and funtional processes than in species composition. For instance, creosotebushbecame dominant over many million of hectares of the Chihuahuan, Sonoran, and MojaveDeserts over a short period of 11,000 years, but a limited number of generations precludesestablishment of highly integrated and biologically regulated communities by co-evolution.Dramatic shifts in species composition of eastern deciduous forests of North America occured


in prehistory and continue into the present. Similar changes are noted in the constantassembling and reassembling of species in the purportedly ancient and stable forests of thetropics. Numerous introductions with few extinctions in the flora of California have increasedspecies richness and probably diversity, and many recent additions are primary contributors toecosystem productivity. Recognition that rangeland ecosystems persist in unstable rather thanstable compositions provides both a challenge and an opportunity for natural resourcemanagement. The challenge is to develop new management principles that incorporatenonequilibrium theory. The opportunity is the promotion of policies and regulations that moreclosely reflect reality.

208

Kaushal, B.R. and Vats, L.K. (1983): Population dynamics and biomass production ofaboveground insects in a tropical grassland. Proceedings of the Indian Academy of Science(Animal Science) 92:447-452.

Keywords: insects; grassland; India; ecosystems.

Abstract. Population dynamics and aboveground insects were studied in a tropical grassland.A total of 30 species belonging to five insect orders viz., Odonata, Mantoidea, Blattoidea,Neuroptera and Diptera were collected. Maximum population density and biomass values onstands I and II were determined.

209

Mellink, E. (1991): Bird communities associated with three traditional agroecosystems in theSan Luis Potosí Plateau, Mexico. Agriculture, Ecosystems and Environment 36:37-50.

Keywords: tropical savanna; wild birds; agroecosystems; pests; crop residues; Mexico;grassland; animal-plant interaction; farming systems.

Abstract. The bird communities associated with three traditional dry farming systems, theirborders and their unfarmed surroundings on the San Luis Potosí Plateau, Mexico, werestudied throughout the year. The systems studied were (1) a purely rain-fed field in a grasslandwith shrubs, (2) a field on a bajada irrigated with runoff water in a complex and densecommunity of cacti and shrubs, and (3) a bajío field irrigated with spring moisture and anephemeral wash in a savanna. The results are in agreement with the hypothesis that complexagroecosystems are less susceptible to pest outbreaks than simple ones. There was no typicalcropland avifauna; communities depended on the particular type of agroecosystem and on theoriginal habitat. The foliage height diversity index did not always parallel bird richness, sincethere are factors affecting the latter which do not affect the index. Edge effect was not evidentin this study. Although two agroecosystems had lower richness than their surroundings, thepresence of isolated fields increased regional bird richness.

210

Olsson, G.A., Liljelund, L.-E. and Hedlund, L. (1991): A strategy for the conservation ofbiodiversity. Ambio 20:269-270.

Keywords: biodiversity; ecosystems; sustainability; species diversity.

References 131

Abstract. Conservation of biological diversity is the most important issue for natureconservation. The importance of biological diversity for humankind, and its ecological, social,economical and cultural values are well recognized within societies. One expression of thisrecognition is the negotiations on a new global convention on conservation of biodiversity.Almost 100 developing and developed countries are currently involved in this effort.However, there are diverging views about how to achieve maintenance and conservation ofbiological diversity on the different levels of ecosystems; habitats, species and genes.Generally, two approaches can be recognized. The traditional strategy emphasizesconservation of ecologically sensitive areas by protecting them and by excluding orminimizing human impact. The rationale behind this strategy is that human impact is anegative and disturbing factor that must be minimized. Protection of sensitive areas is highlyimportant and in some specific cases the only possible way to conserve certain species orecosystems. However, the protection of limited areas, especially against the background ofincreasing human population pressures, and thus the increasing demand on land utilization,will never encompass more than a very limited part of the world's biological diversity. Thus,protected areas should only be viewed as refuge sites, and as a complement to other measures.

211

Brose, M. (1988):) Vielfalt als Grundkonzept standortgerechten Landbaus in Zentralbrasilien.Entwicklungsperspektiven Bd. 32. Kassel (Germany): Lateinamerika-DokumentationsstelleFB6, Gesamthochschule Kassel, p. 1-136.

Keywords: agroforestry; Amazon region; farming systems; shifting cultivation; tropical forest;sustainability; ethnobiology.

Abstract. Data available about ethnobiology in Central Brazil are summarized in this book.The author presents indigenous knowledge and traditional land use systems of Indian tribes inorder to enrich the discussion on sustainable and situation-specific farming systems.Descriptions are given of agriculture in the 16th century (chapter 2); ecological knowledge ofthe Kayapó tribe (chapter 3); land use systems in different ecological zones (chapter 4);specific knowledge concerning the use of trees, medicinal plants, soil fertility etc. (chapter 5);and cultural aspects (chapter 6). In the last chapter, the relevance of ethnobiologicalinformation for the development of sustainable farming systems is discussed. (Abstract bybibliography authors)

212

Chapin III, F.S., Schulze, E.D. and Mooney, H.A. (1992): Biodiversity and ecosystemprocesses. Trends in Ecology and Evolution 7:107-108.

Keywords: biodiversity; ecosystems; species diversity.

Abstract. Results of a workshop on 'Biodiversity and Ecosystem Function', held in Bayreuth,Germany in October 1991, are briefly summarized: A major question was whether diversitythat is important to ecosystem processes is best characterized at the level of species or at somebroader level of functional group. The general consensus was that functional groups (= speciesthat have 'similar' effects on ecosystem processes) are useful in organizing our ecologicalunderstanding of diversity, but that the details of functional groups will depend on theecosystem and question under study. A major research challenge is to predict which species in


a community are keystone species or could become so under reasonable scenarios ofenvironmental changes. The workshop provided substantial evidence that biotic diversity atlevels ranging from genetic diversity among populations to landscape diversity is critical tothe maintenance of natural and agricultural ecosystems.

213

Burger, D. (1994): Der Treibhauseffekt: Ursachen, Folgen und Gegenstrategien. entwicklung+ ländlicher raum 28 (1):3-5.

Keywords: atmosphere; carbon cycle; biomass burning.

Abstract. CO2 and other trace gases relevant for the climate contribute to the heating up of theatmosphere. The natural greenhouse effect raised the earth air temperature to an average of18°C and permitted the evolution of life. The additional greenhouse effect caused by man isthreatening today mankind (life on earth) through rising sea levels, shifting of vegetationzones, loss of biodiversity, changing rainfall patterns and stronger and more frequent storms.Counter-strategies must englobe the reducing of energy consumption in industrializedcountries, enhancing the efficient use of energy and promoting alternative energies. Alsowithin agriculture and forestry, there is a potential for developing strategies to counter-act theprocess of CO2-enrichment in the atmosphere.

214

Keller, M., Jacob, D.J., Wofsy, S.C. and Harriss, R.C. (1991): Effects of tropicaldeforestation on global and regional atmospheric chemistry. Climatic Change 19:139-158.

Keywords: deforestation; Amazon region; tropical forest; atmosphere; cattle; biomass burning.

Abstract. A major portion of tropospheric chemistry occurs in the tropics. Deforestation,colonization, and development of tropical rain forest areas could provoke significant changesin emission of radiatively and photochemically active trace gases. A brief review of studies ontrace gas emissions in pristine and disturbed tropical habitats is followed by an effort to modelregional tropospheric chemistry under undisturbed and polluted conditions. Model resultssuggest that changing emissions could stimulate photochemistry leading to enhanced ozoneproduction and greater mineral acidity in rainfall in colonized agricultural regions. Modelresults agree with measurements made during the NASA ABLE missions. Under agriculturalpastoral development scenarios, tropical rain forest regions could export greater levels of N2O,CH4, CO, and photochemical precursors of NOx and O3 to the global atmosphere withimplications for climatic warming.

215

Fan, Song-Miao, Wofsy, S.C., Bakwin, P.S. and Jacob, D.J. (1990): Atmosphere-biosphereexchange of CO2 and O3 in the central Amazon forest. Journal of Geophysical Research95(D10):16851-16864.

Keywords: tropical forest; Amazon region; atmosphere.

Abstract. Measurements of vertical fluxes for CO2 and O3 were made at a level 10 m abovethe canopy of the Amazon forest during the wet season, using eddy correlation techniques.Vertical profiles of CO2 and O3 were recorded continuously from above the canopy to the soil

References 133

surface, and forest floor respiration was measured using soil enclosures. Nocturnal respirationof CO2 by the forest ecosystem averaged 2.57 kg C/ha/h, with about 85% from the forestfloor. During the daytime, CO2 was taken up at a mean rate of 4.4 kg C/ha/h. Net ecosystemuptake of carbon dioxide increased with solar flux by 0.015 (kg C/ha/h)/(W/m2),corresponding to fixation of 0.0076 moles CO2 per mole photons. The relationship betweennet ecosystem exchange and solar flux was virtually the same in the Amazon forest as inforests in Canada and Tennessee. The relatively high efficiency for utilization of light (about30% of the theoretical maximum) and the strong dependance of net CO2 uptake on solar fluxsuggest that light may significantly regulate net ecosystem exchange and carbon storage in thetropical forest. Changes in the distribution of cloud cover, associated for example withclimatic shifts, might induce globally significant changes in carbon storage. Rates for uptakeof O3 averaged 2.3∗ 1011 molecules/cm2/s in the daytime (10 hours, 700-1700 hours), droppingby roughly a factor of 10 during the 14 hours from dusk to dawn. The mean O3 depositionvelocity at 40 m was 0.26 cm/s in the night and 1.8 cm/s in the day. Diurnal variation of O3deposition was regulated both by stratification of the atmospheric boundary layer and bystomatal response to light and water deficit. The total flux of O3 to the forest was limitedlargely by supply from the free troposphere above. Deposition of O3 to the forest canopyappears to be a regionally, and perhaps globally, important sink for tropospheric O3.

216

Nobre, C.A., Sellers, P.J. and Shukla, J. (1991): Amazonian deforestation and regionalclimate change. Journal of Climate 4:957-988.

Keywords: deforestation; tropical forest; pastures; atmosphere; grasses; Amazon region;annual field crops.

Abstract. Large-scale conversion of tropical forests into pastures or annual crops could lead tochanges in the climate. We have used a coupled numerical model of the global atmosphereand biosphere (Center for Ocean-Land-Atmosphere Atmosphere GCM) to assess the effects ofAmazonian deforestation on the regional and global climate. We found that when theAmazonian tropical forests were replaced by degraded grass (pasture) in the model, there wasa significant increase in the mean surface temperature (about 2.5 degrees C) and a decrease inthe annual evapotranspiration (30% reduction), precipitation (25% reduction), and runoff(20% reduction) in the region. The differences between the two simulations were greatestduring the dry season. The deforested case was associated with larger diurnal fluctuations ofsurface temperature and vapor pressure deficit; such effects have been observed in existingdeforested areas in Amazonia. The calculated reduction in precipitation was larger than thecalculated decrease in evapotranspiration, indicating a reduction in the regional moistureconvergence. There was also an increase in the length of the dry season in the southern half ofthe Amazon Basin, which could have serious implications for the reestablishment of thetropical forests following massive deforestation since rainforests only occur where the dryseason is very short or nonexistent. An empirical bioclimatic scheme based on an integratedsoil moisture stress index was used to derive the movement of the savanna-forest boundary inresponse to the simulated climate change produced by large-scale deforestation. Theimplications of possible climate changes in adjacent regions are discussed.


217

Luizao, F., Matson, P., Livingston, G., Luizao, R. and Vitousek, P. (1989): Nitrous oxideflux following tropical land clearing. Global Biogeochemical Cycles 3:281-285.

Keywords: nitrous oxide; deforestation; tropical forest; pastures; Amazon region; atmosphere;South America; ecosystems.

Abstract. The importance of seasonal cycles of N2O flux from tropical ecosystems and thepossibility that tropical deforestation could contribute to a global increase in N2Oconcentrations were assessed by measuring N2O flux from forest, cleared land, and pastureover an annual cycle in the central Amazon. A pasture that had been converted from tropicalforest had three-fold greater annual N2O flux than a paired forest site; similar results wereobtained in other pastures. If these results are general, such tropical pastures represent aglobally significant source of increased N2O.

218

Houghton, R.A., Skole, D.L. and Lefkowitz, D.S. (1991): Changes in the landscape of LatinAmerica between 1850 and 1985. II. Net release of CO2 to the atmosphere. Forest Ecologyand Management 38:173-199.

Keywords: atmosphere; deforestation; shifting cultivation; Amazon region; carbon cycle;South America; pastures; degradation; ecosystems; establishment.

Abstract. Net release of carbon to the atmosphere from deforestation in Latin America wascalculated for the period 1850-1985. Stocks of carbon in vegetation and soils of majorecosystems, and changes in these stocks of carbon as a result of disturbance, were used tocalculate the net annual flux of carbon. Total net release of carbon between 1850 and 1985was about 30x1015 g (range 17-35x1015 g). Land uses responsible for emissions of carbonwere increased areas of pastures (42% of total emissions), croplands (34%), degraded lands(19%), and shifting cultivation (5%). Logging and the establishment of plantations contributedor accumulated negligible amounts of C over this 135-year period. Annual releases of C to theatmosphere increased over the period 1850-1985; half of the total release occurred after 1960.By 1985 net annual release was 0.67x1015 g C (range 0.39 - 0.82x1015 g C). Relativecontributions of different land uses to this flux were different from those over the long-term.The greatest single source of C in 1985 resulted from increases in area of degraded lands(37% of net flux), and the importance of shifting cultivation increased to almost 20%. Therange of estimates calculated here for the current net flux of C is lower than earlier estimates.The range results from uncertainties in rates of land-use change, in types of ecosystemscleared and stocks of C in these ecosystems, and in rates of decay and regrowth of organicmatter associated with land-use change.

219

Burger, D. (1994): Aufforstung und andere forstliche CO2-Strategien. entwicklung +ländlicher raum 28(1):11-15.

Keywords: atmosphere; carbon cycle; reforestation; deforestation; agroforestry.

Abstract. Forestry CO2-soak pits are formed not only by the vegetation cover and therelatively high amount of biomass in the soil but also by the carbon stored in the products.Their effect increases when these products substitute the fossil sources of energy. The

References 135

limitations for the translation into action of forestry CO2-soak pits strategies lie not as much inthe availability of suitable land or of the production techniques, as in the field of organization,management, funding and processing techniques as well as in the continuous existence of thesame general conditions that have lead to the present destruction of forests. The forestry CO2strategies should contribute not only to the CO2 absorption but also to the regionaldevelopment. They should be sustainable and socio-culturally acceptable. According to thesecriteria, various strategies of forest protection and rehabilitation of degraded forest areasshould become the first priority, while the development of timber plantations ranks last in thesame priority list.

220

Goldammer, J.G. (1994): Vegetationsbrände und globales Klima: Wechselwirkungen.entwicklung + ländlicher raum 28(1):6-10.

Keywords: atmosphere; carbon cycle; tropical forest; tropical savanna; subtropics; fireecology; biomass burning.

Abstract. Throughout all vegetation zones of the globe wildfires in forests and othervegetation types and the use of prescribed fires in forestry and agriculture are a non-uniformphenomenon. In the densely populated and industrialized regions, e.g. in Central Europe, evena small forest fire may cause public concern. Traditional use and the desired effects of fire inmodern agriculture has been replaced by mechanical and chemical technologies. In the lesspopulated tropical and subtropical landscapes and in the temperate and boreal zones of NorthAmerica and Eurasia, large-scale use of fire and wildfires are still a common phenomenon.This contribution describes the most important fire regions and fire regimes of the globe andsummarizes the impact of vegetation fires on atmosphere and as well as the possible feedbackmechanisms between a globally changed climate and the occurence of fire.

221

Groot, P. de (1990): Are we missing the grass for the trees? New Scientist 1698:29-30.

Keywords: atmosphere; overgrazing; carbon cycle; tropical savanna; natural grassland;biomass burning.

Abstract. Amazonian rainforest going up in smoke has become a powerful image ofenvironmental destruction and the growing threat from the greenhouse effect. On the otherhand, tropical grasslands have been almost totally ignored, although their capacity to extractcarbon dioxide from the atmosphere is equal to that of tropical rainforests and often exceedsthat of cropping systems. Natural savanna grassland converted into cropping land or degradedby frequent burning and overgrazing is therefore also an important source of net CO2 release.This fact has probably been widely ignored because at least half of the dry matter productionof grasslands is located in the below-ground parts of the plant, which are generally neglectedby common methods of biomass production estimates.

222

Walker, B.H. (1994): Global change strategy options in the extensive agriculture regions ofthe world. Climatic Change 27:39-47.


Keywords: biomass burning; burnings; tropics; methane; cattle; atmosphere; soil erosion;livestock; stocking rate.

Abstract. The extensive agricultural regions contain relatively little of the world's carbon andtheir main influence on atmospheric composition is via biomass burning in the more humidregions of the tropics, and methane from cattle production. In terms of direct feedbackinfluence on climate their effects are via opaqueness of the atmosphere (dust and aerosols) andthe albedo of the surface. Change in these regions is brought about by the separate and(especially) interactive effects of climate, fire and herbivory. Likely changes in productivity,vegetation structure and soil erosion will lead to some changes in stored carbon and feedbackeffects. Possible increased cultivation of marginal areas is an important unknown.Management options include livestock numbers, type and distribution, fire regimes, woodyvegetation clearing, subsistence cropping and rehabilitation measures. Response strategies inline with IPCC goals include reducing stocking rates, halting clearing of woody plants,reducing fire frequencies and (where cropping is practised) use of zero-tillage. A modellingapproach is suggested as a basis for examining which responses are appropriate, given thatmost managers in these regions have very few options and the regions contribute relativelylittle to the control of the world's climate.

223

Dale, V.H., Houghton, R.A. and Hall, C.A.S. (1991): Estimating the effects of land-usechange on global atmospheric CO2 concentrations. Canadian Journal of Forest Research21:87-90.

Keywords: atmosphere; Asia; land-use changes.

Abstract. Determining how land-use change effects atmospheric CO2 concentrations requiresnew approaches to research because of the large area and the long period of time involved.This special issue of the Canadian Journal of Forest Research presents a series of papers thatdemonstrate one approach to the problem. Estimates of the flux of carbon to the atmosphereare based on site-specific information concerning the effects of land-use change on the carboncontent of terrestrial vegetation. This spatially explicit approach combines historical andcurrent information on land-use change for a specific area. South and southeast Asia waschosen for the study because the region is undergoing major land-use changes and makes asignificant contribution to atmospheric CO2. The results of the study have assisted in reducingthe uncertainty about the magnitude of carbon release while providing new constraints to theanalysis.

224

Haas, G., Geier, U., Schulz, D. and Koepke, U. (1994): Die CO2-Effizienz des OrganischenLandbaus - Chancen für die Entwicklung landwirtschaftlicher Produktionssysteme in derDritten Welt? entwicklung + ländlicher raum 28(1):25-29.

Keywords: fertilizers; nitrogen fixation; legumes; tropics; subtropics; farming systems;ecosystems; agroforestry; carbon cycle; energy balance; atmosphere.

Abstract. Comparison between organic and conventional plant production in Germany revealssavings of fossil energy and thus CO2-emissions of 61 per cent. This is basically due to thefact that mineral nitrogen fertilizers are not used. The method of ensuring nitrogen supply bynitrogen fixation through legume symbiosis can be adapted anywhere in the world. A further

References 137

main area of fossil fuel consumption in the agriculture of the industrialized countries is causedby the intensive use of machinery. In countries with large manpower resources in rural areas,savings can be made by developing labour-intensive production systems. To calculate theCO2-binding capacities when comparing the systems, the sum of all CO2-sinks in the systemshas to be included. As well as the bound carbon contained in crops actually harvested, thisalso includes catch crops, underseeds, harvest remains and roots. High soil C-contents inorganic farming increase not only the soil fertility but also the reduction function of thesystem. For the respective site-specific conditions in the countries of the tropics and sub-tropics, farming systems are to be developed which imitate natural ecosystems, as here forexample "standing C-sinks" can be established on the basis of rain forests, inter alia in theform of agroforestry systems. The agricultural policies pursued by developing countries todate have been based on the guiding principle of conventional farming making intensive useof external inputs, as practised in the industrialized countries. In view of the economic andecological problems caused by conventional farming, organic farming is currently becomingincreasingly widespread in North America and Europe. The productivity of organic farmingachieved in these countries through intensive development work is virtually the same theworld over, i.e. is sufficient to feed the population. More efficient use of natural resources inorganic farming and system-immanent environmentally and climatically sound production arenow integral approaches in the development of site-appropriate production systems indeveloping countries.

225

Escobar, C.J. and Toriatti D., J.L. (1991): Distribución de la materia orgánica y delcarbono-13 natural en un Ultisol del piedemonte amazónico. Pasturas Tropicales 13(2):27-30.

Keywords: pastures; Colombia; soil chemical properties; soil organic matter; tropical forest;South America; Amazon region.

Abstract. The distribution of natural soil carbon (C-13) and its changes as a result of cuttingforest and then planting pasture were studied in two areas of an Ultisol from Caquetá,Colombia. The study site had perudic moisture and isohyperthermic temperature regimes. Onesite was under forest (P0) and the other site had been deforested and cultivated with Paspalumnotatum (P15) for 15 years. Soil physical, chemical and mineralogical characteristics at the twosites were very similar. Morphological differences observed could be related to soilmanagement. Total C content decreased with depth in the two profiles. The quantity of carbonlost was around 57.5 tons/ha of C in the pasture system, after 15 years of use. The δ13C valuesare about -29‰ in 0-0.34 m of the profile under forest, and about -19‰ in the 0.14 m layersof the profile under pasture. On layers of 0.14-0.30 m, this value was -25‰. The δ13C

values

were used to estimate the quantities of C derived from forest and from pasture. Carbonderived from pasture represented, between 64.6% in surface and 29.5% in depth, of the totalcarbon at P15.

226

Crutzen, P.J., Aselmann, I. and Seiler, W. (1986): Methane production by domesticanimals, wild ruminants, other herbivorous fauna, and humans. Tellus 38B:271-284.

Keywords: atmosphere; cattle; methane.


Abstract. A detailed assessment of global methane production through enteric fermentation bydomestic animals and humans is presented. Measured relations between feed intake andmethane yields for animal species are combined with population statistics to deduce a currentyearly input of methane to the atmosphere of 74 Tg (1 Tg = 1012 g), with an uncertainty ofabout 15%. Of this, cattle contribute about 74%. Buffalos and sheep account for 8-9%, and theremainder stems from camels, mules and asses, pigs, and horses. Human CH4 production isprobably less than 1 Tg per year. The mean annual increase in CH4 emission from domesticanimals and humans over the past 20 years has been 0.6 Tg, or 0.75% per year. Populationfigures on wild ruminants are so uncertain that calculated CH4 emissions from this source mayrange between 2 Tg and 6 Tg per year. Current CH4 emission by domestic and wild animals isestimated to be about 78 Tg, representing about 15-25% of the total CH4 released to theatmosphere from all sources. The likely CH4 production from domestic animals in 1890 wasabout 17 Tg, so that this source has increased by a factor of 4.4. A brief tentative discussion isalso given on the potential CH4 production by other herbivorous fauna, especially insects.Their total CH4 production probably does not exceed 30 Tg annually.

227

Leng, R.A. (1991): Digestive physiology of ruminants: implications for improving animalproduction from poor quality forages. In: Leng, R.A. (ed.), Improving ruminant productionand reducing methane emissions from ruminants by strategic supplementation. Washington,D.C., USA: United States Environmental Protection Agency (EPA), EPA/400/1-91/004. p.43-52.

Keywords: methane; cattle; forage quality; atmosphere.

Abstract. The information given in this chapter is fundamental to understanding the strategiesfor limiting methane production from ruminants. Aspects covered include anatomy of theruminant, the microbiology of the rumen, the requirements of rumen microorganisms fornutrients and the stoichiometry of rumen fermentative digestion of feed and the balances ofnutrients available to the animal. Practical implications of the balances of protein to energy inthe digestion products that are absorbed are discussed. (Abstract by bibliography authors)

228

Leng, R.A. (1991): Modifying methane production. In: Leng, R.A. (ed.), Improving ruminantproduction and reducing methane emissions from ruminants by strategic supplementation.Washington, D.C., USA: United States Environmental Protection Agency (EPA), EPA/400/1-91/004. p. 53-71.

Keywords: methane; cattle; forage quality; atmosphere.

Abstract. Two factors affect methane production per unit of digestible feed; these aremicrobial growth efficiency and the formation of propionate in the rumen. Higher productionof either cells or propionate reduces methane production per unit of organic matter digested inthe rumen. Microbial growth efficiency is inefficient in animals fed on forage based diets,typical of those fed to ruminants in developing countries, and can be stimulated by nutrientsupplementation. This reduces methane generation markedly. Factors that limit the efficiencyof microbial growth in the rumen are discussed. Ruminants use low-digestibility forages moreefficiently when their protein status is improved by supplementation with a bypass protein.Methane production per unit of production, therefore, can be ameliorated in practice by

References 139

balancing the nutrient available from rumen fermentation with dietary protein that avoidsfermentation. The implications of improving both feed conversion efficiency and growth rate,for the rates of methane production per animal or per unit of product are outlined. (Abstract bybibliography authors)

229

Holter, J.B. and Young, A.J. (1992): Methane prediction in dry and lactating Holstein cows.Journal of Dairy Science 75:2165-2175.

Keywords: methane; dairy cows; feed supplements; forage quality; production level;atmosphere.

Abstract. Data from six experiments (two with dry cows) were used to predict partitioning ofgross energy to CH4 in Holstein cows using selected independent variables, some of whichwere intercorrelated, and a stepwise backward elimination regression procedure. Methaneoutputs ranged from 3.1 to 8.3% (mean 5.5) of gross energy intake for 134 dry cow balancetrials and from 1.7 to 14.9% (mean 5.2) of gross energy intake for 358 lactating cow energybalance trials. This is equivalent to 176 and 300 g/d or 245 and 419 L/d of CH4 for dry andlactating Holstein cows, respectively. Digestibilities of hemicellulose and neutral detergentsolubles were positive predictors, and cellulose digestibility was a negative predictor of CH4output in dry cows fed all forage diets, but hemicellulose digestibility was not a significantvariable for predicting CH4 production by lactating cows fed diets with concentrate andforages. Fiber digestibility generally remained in models to predict CH4 output. Except for onedata set, regression equations accounted for 50 to 72% of the variation in percentage of grossenergy partitioned to CH4 by Holstein cows. Results confirm that increased concentratefeeding reduces CH4 production. Supplementation of lactation diets with fat generallyincreases fat digestibility, and this trait was associated with reduced CH4 output. Resultsenable 1) estimation of CH4 output for calculation of metabolizable energy and 2)computation of the contribution from dairy cows to global warming.

230

Tamminga, S. (1992): Nutrition management of dairy cows as a contribution to pollutioncontrol. Journal of Dairy Science 75:345-357.

Keywords: dairy cows; pollution; methane; production level; forage quality; atmosphere;nitrogen.

Abstract. Dairy production causes unavoidable losses in respiration, faeces, and urine, whichmay become an environmental burden as contributors to the "greenhouse" effect (CO2, CH4)or to the pollution of air (NH3), soil surface, and sub-soil water ( NO3

− , P). Losses inrespirations can be reduced by increasing feed quality and level of production. Increased feedquality can reduce losses in methane, whereas an increased level of production decreases therelative losses in maintenance. Faecal and urinary losses can be reduced by minimizing theintake of N and P relative to energy. Further reductions can result from increasing feed qualityand level of production, from matching or synchronizing the availability of N and energy inthe rumen, and from shifting the site of digestion of protein and starch from the rumen to thesmall intestine. Improved feed quality will reduce endogenous protein losses. In order toexploit fully the potential of nutritional management in pollution control, computer simulationmodels describing dairy production in a dynamic way are needed.


231

Pelchen, A. and Peters, K.J. (1994): Schadgase aus der Tierhaltung - Auswirkungen auf denTreibhauseffekt. entwicklung + ländlicher raum 28(1):20-24.

Keywords: methane; cattle; atmosphere; forage quality.

Abstract. The importance of animal husbandry for global warming is rather small. The shareof 4 per cent is not significant compared to other sources of greenhouse gases. On the otherhand the husbandry of ruminants is inseparably linked to methane emissions and they can onlybe influenced within tight borders. Main factors are quantity, quality and digestibility of feedsas well as the energy supply to the animal: A reduction of crude fibre in the ration reduces theemissions of methane. An increase in digestibility decreases the production of methane perunit of gross energy (GE) at feeding levels of three times maintenance, but increases it forlower levels of feeding. An enlargement of the energy supply from maintenance to multiplesof maintenance reduces the energy loss per unit of gross energy via methane. According tothese facts the principle "More performance - less methane" comprises the main issue toreduce methane emissions. Anything enhancing the yield of milk and meat from the singleanimal diminishes the rate of methane emissions per unit of desired product, because it allowsa reduction in total animal numbers. Special measures for the developing countries have to betaken, to make sure that necessary future expansions in the production are not achieved by anincrease in herd sizes but by a growth of the performance of the single animal. The potentialfor a reduction of methane emissions in the developing countries is much higher than in theindustrialized countries.

232

Matthews, R.B., Kropff, M.J. and Bachelet, D. (1994): Climate change and rice productionin Asia. entwicklung + ländlicher raum 28(1):16-19.

Keywords: rice; South East Asia; methane; atmosphere.

Abstract. Rice is the second most important crop in the world after wheat, with about 522million tons being produced from about 148 million hectares in 1990. The largest productionof rice is from Asia, which produces about 94 per cent of the total world production. In thisregion, rice is the main item of the diet, and provides an average of 35 per cent of the totalcalorific intake compared to only 2 per cent in the US. Rapid population growth is alreadyplacing increasing pressure on the rice-growing resources in the region, not only from theincreased demand from a higher number of people to feed, but also from the encroachment ofresidential areas into rice growing areas. The effects of climate change only add to an alreadycomplex problem, even more so as rice cultivation itself has a significant effect on globalwarming through the emission of the greenhouse gas, methane, from decaying plant materialin the water-logged paddy fields. There is clearly an urgent need to evaluate the interactionbetween climate change and rice production in this region to provide a basis for decisions bypolicy makers, agriculturalists and environmentalists alike.

References 141

233

Fisher, M.J., Rao, I.M., Ayarza, M.A., Lascano, C.E., Sanz, J.I., Thomas, R.J. and Vera,R.R. (1994): Carbon storage by introduced deep-rooted grasses in the South Americansavannas. Nature 371:236-238.

Keywords: grasses; savanna; pastures; South America; land-use changes; burnings;atmosphere; carbon cycle; introduced species.

Abstract. Estimates of the global carbon dioxide balance have identified a substantial 'missingsink' of 0.4-4.3 Gt per year. It has been suggested that much of this may reside in theterrestrial biosphere. Here we present an analysis of the carbon stored by pastures based ondeep-rooted grasses which have been introduced in the South American savannas. Althoughthe deep-rooted grasses were chosen principally for agricultural reasons, we find that they alsosequester significant amounts of organic carbon deep in the soil. If our study sites arerepresentative of similar pastures throughout South America, this process could account forthe sequestration of 100-507 Mt carbon per year - a substantial part of the 'missing sink'. Thus,although some land-use changes (such as burning tropical rainforests) contribute to theatmospheric CO2 burden, we conclude that the introduced pastures studies here help to offsetthe effect of anthropogenetic CO2 emissions.

234

Haiger, A. (1993): Naturgemäße Milchviehzucht. In: Zerger, U. (ed.), Forschung imökologischen Landbau. Bad Dürkheim/Germany: Stiftung Ökologischer Landbau (SÖL), p.57-63.

Keywords: sustainability; dairy cows; production level; breeding.

Abstract. Ruminants play an important role for different kinds of land-use systems: Theymake use of plants like forage legumes and grasses that are essential for the sustainability ofmany agricultural systems, or of landscapes that are unsuitable for other forms of agriculturalexploitation than grazing. In a 5-year average of a cow producing 4500 kg milk/yr, 1 kg offodder protein yields about 430 g of milk protein. For meat production, this relation is only 1kg : 120 g in the case of beef cattle and 1 kg : 180 g in the case of swine. Selecting cows forhigher individual milk yields per time unit is an efficient measure to save fodder and labourcosts, resulting in reduced energy needs per kg milk produced. A cow producing 5000 kgmilk/yr needs 38% less energy per kg milk than an animal yielding 2000 kg in the same timeperiod. A further increase of another 3000 kg (to 8000 kg/yr) reduces the energy needs per kgmilk produced only by 10%. On the other hand, cows with this production level needincreasing amounts of concentrates to meet their energy requirements. Very high individualproduction levels therefore depend on fossil energy used for cheap production of concentrates.Individual milk yields of more than 7000 kg/yr imply surplus nitrogen in the fodder ration,resulting in a potential danger of groundwater pollution. The author therefore suggests anecological range of individual milk yields, the optimum being between 5000 and 7000kg/animal/yr. Furthermore, corresponding criteria for selection and breeding of milk cows arediscussed. (Abstract by bibliography authors)

235

Fajer, E.D., Deane Bowers, M. and Bazzaz, F.A. (1989): The effects of enriched carbondioxide atmospheres on plant-insect herbivore interactions. Science 243:1198-1200.


Keywords: atmosphere; insects; insect-plant interaction; pest development.

Abstract. Little is known about the effects of enriched CO2 atmospheres, which may exist inthe next century, on natural plant-insect herbivore interactions. Larvae of a specialist insectherbivore, Junonia coenia (Lepidoptera: Nymphalidae), were reared on one of its host plants,Plantago lanceolata (Plantaginaceae), grown in either current low (350 ppm) or high (700ppm) CO2 environments. Those larvae raised on high-CO2 foliage grew more slowly andexperienced greater mortality, especially in greater instars, than those raised on low-CO2foliage. Poor larval performance on high-CO2 foliage was probably due to the reduced foliarwater and nitrogen concentrations of those plants and not to changes in the concentration ofthe defensive compounds, iridoid glycosides. Adult pupal weight and female fecundity werenot affected by the CO2 environment of the host plant. These results indicate that interactionsbetween plants and herbivorous insects will be modified under the predicted CO2 conditionsof the 21st century.

236

Fungameza, D.B. (1991): Agroforestry and ecofarming practices for soil conservation inKigoma Tanzania. Göttinger Beiträge zur Land- und Forstwirtschaft in den Tropen undSubtropen, Vol. 63, Göttingen (Germany): E. Goltze Verlag, 264 p.

Keywords: agroforestry; soil erosion; intercropping; maize; beans; yields; weed control;fertilizers; improved fallow; natural fallow; green manure; Leucaena leucocephala; legumetrees; shrubs; Crotalaria ; Tephrosia vogelii; Calliandra calothyrsus; Flemingia macrophylla;Albizia lebbeck; Cassia siamea; Mucuna utilis; Cassia spectabilis; Tanzania; Africa; tropicalhighlands.

Abstract. This research work focussed on soil erosion in Kigoma, Tanzania and/or preventionor control measures. An interdisciplinary approach was followed. A methodology whichcombined diagnosis and design and user perspective was used to detect constraints andopportunities existing within the land use systems practiced in the area. The aproach requiredthe analysis of the physical environment, socio-economy, population patterns, land usesystems with household supply problems, production and conservation constraints. Morefocus was put on the needs of different land users. The severity and causes of soil erosionwere assessed qualitatively and these were matched to the needs of the people in order tohighlight agroforestry and ecofarming practices for soil conservation. The productivity ofcandidate technologies was tested either on station or direct in collaboration with villagers.The following results were obtained: 1. Intercropping maize with beans on the same ridge in aridge-furrow ("matuta") system did not affect the yields of the former. The yields of beanswere significantly depressed by 68-90%. The best Land Equivalent Ratios and Area TimeEquivalent Ratios were obtained when beans and maize were intercropped in parallel rows. 2.Sowing maize on top of the ridges and broadcasting in the furrows the seeds of Crotalariajuncea and C. retusa at the rate of 50 kg/ha decreased significantly the amount of weeds by62-74% during the first weeding and had no effect on the yields of maize. 3. Depending on theamount of biomass added in the furrows, Crotalaria ochroleuca and C. retusa increased theyields of succeeding maize crop by 62-168% and by 79-184% over the control, respectively.Highest maize yields were obtained by combination of this treatment with mineral fertilizeraddition. 4. Tephrosia vogelii fallow accumulated 195 kg N/ha. Incorporating the biomass intothe soil increased significantly the yields of subsequent maize crop by 2.5 time over thenatural fallow. 5. Calliandra calothyrsus hedgerows yielded 11.12 and 17.97 t/ha dry matterduring the first and second year, respectively. The use of C. calothyrsus green manure raised

References 143

significantly the yields of hedgerow intercropped maize by 74 and 96% over the control andwere 71% of the yields obtained in a fertilizer treatment. Combined use of green manure andfertilizer resulted in significantly higher (33-34%) maize yields than the fertilizer check. 6.Three year-old Albizia lebbek and Leucaena leucocephala tree lines did not affect the yields ofmaize planted in their vicinity. 7. Cassia siamea trees planted scattered on crop land improvedtopsoil chemical properties under their canopies. There was an increase in soil pH, organiccarbon, total N, total P, exchangeable K, Ca and Mg. But yields of maize planted under thefertile canopies of C. siamea were depressed by 79%. 8. Whereas trees and shrub speciesfound in the natural Miombo woodland were growing slowly at the rate of 0.75-1.25 cm peryear, planted multipurpose species showed mean diameter increments which ranged from 1.39cm per year for Syzygum cumini to 4.99 cm for Albizia lebbek. Mean annual height incrementswere in the range of 0.82 m in the case of S. cumini to 4.58 m in the case of Cassiaspectabilis. The survival of trees planted by different land users was poor (0-21%) oncommunal lands, fair (25-68%) by individuals and good (60-89%) in schools. (Abstract bybibliography authors)

237

Bourgoing, R. (1990): Choix et méthode d'établissement de la plante de couverture pour laculture du cocotier hybride en milieu villageois. Oléagineux 45:23-30.

Keywords: fallow; erosion; fertility; cover crops; weeds; legumes; Centrosema pubescens;Calopogonium mucunoides; Pueraria javanica.

Abstract. Hybrid coconut plantations on smallholdings are usually located on land used forgrowing food crops or on land which was formerly cultivated then abandoned and left fallow.In the former case, the plantations have become highly susceptible to erosion, and in the lattercase, they have been invaded by Imperata. In both cases, the soils have lost much of theirfertility. Recuperation of such land for hybrid coconut growing requires the use of appropriatesoil conservation techniques. One of the best known soil conservation techniques - planting agood cover crop before or at the same time as the coconuts are planted - is capable ofimproving the structure and fertility of the soil within a short time, whilst controlling erosionand perennial weed development. A description of the most widely used legume species(Centrosema pubescens, Calopogonium mucunoides, C. caeruleum, Pueraria javanica,Psophocarpus palustris, Flemingia macrophylla), their main characteristics, growingmethods, as well as management practices are given in this paper. (Abstract by bibliographyauthors)

Chapter 7: List of keywords144

7 List of keywords

acid soil 23, 33, 34, 35, 44, 53, 62, 67, 72,112, 114

adapted germplasm 33, 69, 86, 87, 99, 100Aeschynomene americana 17, 44, 89, 90,

102, 103Africa 33, 35, 36, 38, 39, 45, 53, 55, 72,

75, 84, 86, 87, 88, 99, 142agroecosystems 18, 44, 130agroforestry 10, 15, 21, 29, 36, 37, 39, 40,

56, 69, 70, 77, 79, 80, 86, 93, 108, 110,112, 131, 134, 136, 137, 142

agropastoral systems 40, 53, 54Al decrease 63Albizia lebbeck 17, 115, 142allelopathy 25, 36, 93, 94alley cropping 6, 15, 29, 33, 34, 35, 40,

52, 56, 57, 84, 86Alnus japonica 40Alysicarpus vaginalis 55, 89Amazon region 34, 36, 37, 40, 51, 52, 56,

59, 69, 70, 71, 104, 110, 111, 113, 119,131, 132, 133, 134, 137

Anacardium occidentale 110Andropogon gayanus 16, 82, 85animal production 12, 30, 37, 42, 46, 52,

59, 70, 74, 86, 94, 100, 108, 124, 128,138

annual field crops 36, 39, 40, 43, 46, 53,54, 57, 58, 78, 79, 85, 86, 91, 105, 107,133

ants 11, 18, 24, 91, 97, 98Arachis pintoi 84, 89, 96Asia 40, 45, 84, 88, 97, 98, 99, 136, 140atmosphere 3, 27, 30, 74, 132, 133, 134,

135, 136, 137, 138, 139, 140, 141, 142Australia 6, 12, 18, 20, 21, 26, 42, 43, 53,

54, 58, 61, 62, 63, 64, 67, 68, 73, 77, 78,80, 86, 91, 99, 100, 105, 107, 108, 109,117, 124, 128, 129

beans 39, 57, 79, 114, 142Bertholletia excelsa 110, 111biodiversity 2, 3, 24, 25, 26, 27, 67, 118,

119, 120, 121, 122, 125, 130, 131, 132

biological control 17, 18, 88, 91, 96, 97,98

biomass burning 28, 132, 135, 136birds 24, 27, 125, 130Bixa orellana 110Boophilus microplus 18, 92Brachiaria 23, 37, 50, 66, 70, 71, 75, 81,

82, 84, 94, 113Brachiaria decumbens 70, 81, 84Brachiaria humidicola 23, 37, 71, 82, 113Brazil 67, 71, 91, 97, 100, 110, 111, 119,

131breeding 19, 36, 80, 87, 102, 141bumble bees 117burnings 63, 136, 141Byrsonima crassifolia 110Cajanus cajan 18, 34, 35, 39, 52, 56, 66,

88, 90California 65, 93, 120, 130Calliandra calothyrsus 142Callosobruchus maculatus 98Calopogonium mucunoides 14, 18, 49,

143Cameroon 41, 79Canavalia ensiformis 18, 91carbon cycle 12, 32, 62, 132, 134, 135,

136, 141cassava 35, 40, 52, 66, 79, 92, 114Cassia siamea 116, 117, 142, 143Cassia spectabilis 142cation exchange capacity 4, 46, 50, 60, 66cattle 8, 10, 17, 18, 19, 21, 28, 29, 30, 31,

32, 34, 36, 37, 42, 46, 52, 55, 57, 59, 68,69, 71, 72, 79, 80, 81, 82, 87, 92, 97,109, 111, 125, 126, 132, 136, 137, 138,140, 141

Cedrela odorata 110, 111Centrosema 14, 18, 33, 41, 45, 47, 49, 50,

55, 66, 82, 83, 84, 88, 89, 96, 99, 102,104, 143

Centrosema acutifolium 49, 89Centrosema brasilianum 99

List of keywords 145

Centrosema macrocarpum 41, 49, 84, 89Centrosema pascuorum 55, 102Centrosema pubescens 14, 18, 33, 45, 47,

49, 66, 82, 83, 84, 89, 102, 104, 143cereals 39, 43, 90chemical composition 16, 27, 44, 124, 125Chloris gayana 65, 95Cochliobolus sativus 18, 91Coleoptera 98Collembola 67Colletotrichum gloeosporioides 100Colombia 37, 49, 52, 59, 67, 69, 81, 84,

91, 96, 97, 98, 99, 100, 123, 137cover crops 4, 8, 9, 16, 17, 18, 44, 46, 47,

49, 50, 51, 65, 66, 88, 143cowpea 37, 51, 66, 76, 85, 98crop residues 40, 109, 130crop rotation 8, 9, 36, 46, 65, 91, 114, 115Crotalaria 18, 48, 52, 65, 88, 90, 142cultivation methods 112Cynodon 17, 36, 47, 50, 88deforestation 20, 21, 22, 25, 31, 36, 37,

63, 69, 70, 71, 76, 84, 93, 104, 105, 107,110, 119, 121, 122, 123, 132, 133, 134

degradation 3, 7, 11, 13, 22, 25, 26, 28,31, 32, 34, 37, 59, 60, 61, 64, 69, 70, 71,77, 80, 84, 86, 108, 109, 110, 111, 113,114, 118, 119, 122, 123, 134

denitrification 12, 29, 68, 69, 74desertification 13, 22, 31, 109, 112deserts 86, 98, 112, 126, 129Desmodium ovalifolium 14, 18, 37, 40, 49,

82, 84, 89, 92, 95, 99Dioscorea alata 57disease control 91disease resistance 99, 100diseases 3, 17, 18, 19, 23, 27, 32, 37, 40,

69, 87, 88, 91, 94, 95, 96, 99, 100drainage 11, 20, 22, 74, 117earthworms 9, 11, 14, 27, 42, 66, 68, 73,

74, 83economics 52, 67, 79, 108, 109, 119, 121,

122

ecosystems 4, 10, 12, 17, 18, 20, 22, 23,24, 27, 28, 32, 59, 69, 72, 87, 88, 99,103, 108, 109, 110, 111, 112, 113, 116,118, 119, 120, 121, 129, 130, 131, 132,134, 136, 137

Ecuador 40, 104energy balance 79, 136England 37, 67, 68erosion 2, 3, 8, 10, 12, 13, 14, 15, 20, 22,

24, 25, 31, 32, 33, 36, 37, 38, 40, 48, 49,50, 55, 58, 69, 70, 75, 76, 77, 78, 79, 80,83, 84, 85, 86, 88, 103, 104, 106, 108,112, 114, 115, 125, 136, 142, 143

erosion control 3, 15, 24, 32, 36, 40, 48,50, 58, 69, 70, 75, 76, 77, 78, 79, 80, 83,84, 85, 86, 114

Erythrina 56establishment 2, 23, 24, 28, 31, 40, 49, 53,

55, 59, 70, 71, 77, 84, 92, 97, 107, 108,109, 110, 111, 112, 113, 114, 115, 116,117, 129, 134

ethnobiology 131Eucalyptus 17, 79, 105, 114, 116, 117evaluation methods 100evolution 25, 26, 67, 124, 128, 129, 132fallow 4, 12, 13, 15, 33, 34, 35, 37, 38, 39,

40, 41, 42, 43, 50, 51, 53, 55, 63, 64, 79,88, 90, 91, 92, 142, 143

farming systems 3, 4, 15, 17, 29, 31, 33,35, 41, 43, 45, 46, 55, 64, 66, 72, 74, 77,79, 86, 109, 128, 130, 131, 136, 137

feed supplements 80, 124, 139fertility 4, 6, 7, 9, 10, 11, 12, 13, 25, 31,

33, 34, 37, 38, 39, 40, 41, 43, 47, 52, 54,55, 57, 59, 63, 67, 68, 75, 77, 79, 84,123, 131, 137, 143

fertilization 25, 36, 42, 47, 51, 52, 59, 60,62, 68, 69, 72, 74, 106, 107, 113, 114

fertilizers 12, 21, 23, 25, 28, 33, 36, 43,49, 50, 52, 53, 60, 78, 112, 116, 136,142

Ficus poacellii 79fire ecology 135Flemingia macrophylla 15, 16, 65, 93,

142flooding 20, 104


Florida 21, 22, 89, 102, 103, 106fodder banks 53forage legumes 5, 6, 33, 38, 39, 41, 55, 84,

86, 96, 102, 141forage quality 32, 113, 138, 139, 140forage trees 69, 70, 80, 86, 123fruit orchards 47fruit trees 79, 110fuelwood 13, 37, 40, 79, 80, 122fungal diseases 18, 69, 91, 95, 99, 100genetic erosion 25, 88genetics 87, 88, 118, 121, 122germplasm 19, 25, 33, 69, 86, 87, 88, 99,

100, 108, 114Gliricidia sepium 15, 33, 38, 40, 57, 58,

65, 79, 86, 93, 115Glycine wightii 66, 95granivory 98, 116grasses 5, 6, 7, 8, 9, 13, 15, 16, 17, 26, 29,

42, 43, 45, 47, 48, 49, 50, 52, 54, 55, 61,62, 65, 66, 67, 69, 71, 75, 77, 79, 83, 84,87, 91, 93, 94, 95, 96, 97, 99, 101, 110,111, 112, 113, 114, 115, 116, 117, 124,125, 126, 127, 129, 133, 141

grasshoppers 19, 101grassland 8, 9, 11, 19, 36, 45, 65, 66, 67,

68, 72, 73, 75, 94, 97, 101, 108, 115,120, 123, 124, 125, 128, 130, 135

grazing 8, 10, 13, 15, 16, 19, 21, 22, 25,26, 27, 31, 34, 40, 42, 52, 59, 61, 67, 70,71, 72, 73, 75, 77, 79, 80, 81, 82, 83, 87,94, 96, 97, 100, 101, 102, 108, 109, 112,114, 115, 116, 118, 120, 123, 124, 125,126, 127, 128, 141

green manure 4, 14, 15, 39, 43, 44, 45, 48,84, 89, 90, 142

ground cover 14, 44, 51, 58, 77, 78, 83,84, 85, 114

groundwater 20, 22, 30, 74, 105, 107, 141groundwater level 22, 105, 107Helianthus annuus 58, 78herbivory 24, 26, 116, 124, 125, 126, 127,

136Heterodera glycines 17, 89Heteropsylla cubana 97, 98, 99, 108

Hevea brasiliensis 49Hibiscus tiliaceus 79hydrology 3, 68, 69, 75, 82, 103, 104, 106Hyparrhenia rufa 23, 96, 113Imperata cylindrica 18, 41, 48improved fallow 29, 33, 34, 35, 37, 38, 51,

88, 142improved pastures 6, 9, 18, 28, 52, 60, 61,

67, 78, 80, 92, 105, 108, 109, 113India 106, 112, 118Indigofera endecaphylla 91Indigofera hirsuta 17, 44, 90, 91Indigofera suffruticosa 91Indigofera truxillensis 91Indonesia 79infiltration 8, 11, 13, 14, 15, 20, 32, 50,

65, 66, 75, 76, 77, 78, 80, 82, 83, 87,106

Inga edulis 37, 40, 56, 92insect pests 18, 19, 69, 88, 91, 96, 97, 101insect pollination 117insects 19, 24, 27, 40, 73, 88, 96, 97, 102,

125, 130, 142intercropping 14, 34, 37, 38, 39, 55, 86,

89, 93, 114, 115, 142introduced species 67, 68, 113, 129, 141invertebrates 11, 67, 73, 116, 118land restoration 113, 115Lannea coromandelica 79leaching 6, 7, 10, 12, 22, 40, 46, 54, 59,

60, 62, 68, 69, 109legume trees 34, 35, 37, 40, 56, 57, 65, 77,

79, 80, 86, 108, 142legumes 5, 6, 7, 8, 9, 10, 12, 14, 18, 22,

23, 24, 29, 30, 31, 33, 34, 35, 38, 39, 40,41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 66,67, 69, 77, 78, 79, 80, 83, 84, 86, 88, 89,90, 91, 92, 94, 95, 96, 97, 98, 99, 100,102, 108, 109, 110, 112, 113, 114, 115,117, 129, 136, 141, 143

Leucaena leucocephala 15, 16, 33, 34, 39,40, 65, 79, 84, 86, 93, 95, 96, 97, 99,108, 115, 142, 143


ley farming 6, 35, 43, 46, 54, 59, 63, 67,109, 117

lignin 5, 8, 16, 44, 56live mulch 33, 35, 44, 48, 49, 50, 51, 83,

84livestock 2, 3, 15, 20, 24, 31, 32, 37, 39,

41, 45, 55, 67, 76, 78, 79, 80, 83, 84, 88,106, 108, 112, 116, 118, 122, 123, 125,136

maize 33, 34, 35, 37, 39, 41, 44, 47, 48,50, 51, 53, 55, 57, 64, 66, 72, 83, 92,142

manure 8, 14, 15, 39, 43, 44, 45, 48, 55,57, 72, 79, 84, 89, 90, 116, 142

marginal lands 86, 100, 109, 112Medicago sativa 18, 48, 64, 106Medicago scutellata 58Melinis minutiflora 66, 114Meloidogyne arabicida 17, 89Meloidogyne arenaria 17, 89, 90, 95Meloidogyne incognita 18, 88, 90Meloidogyne spp. 37, 95, 102, 103Methane 29, 137, 138, 139Mexico 74, 82, 130microclimate 2, 3, 32, 86micronutrients 13, 49millet 76, 85, 91Mimosa invisa 49mineral nutrients 40, 59mineralization 5, 8, 11, 42, 44, 56, 68, 71mining 22, 64, 118mixed farming 31, 36, 37, 41, 55, 72, 79,

117models 22, 117, 119, 122, 123, 126, 128,

139moisture collection 86, 112Mucuna utilis 142mulch 14, 15, 16, 33, 35, 44, 48, 49, 50,

51, 52, 57, 58, 65, 66, 83, 84, 86, 93,117

mycorrhiza 11, 109, 114, 115, 116natural fallow 35, 36, 38, 41, 53, 92, 93,

142natural grassland 26, 108, 135

natural pastures 27, 53, 79, 124, 128nematodes 18, 19, 33, 37, 88, 89, 90, 95,

96, 99, 102, 103Nigeria 34, 38, 47, 53, 66, 72, 86, 88, 98,

104nitrogen 4, 5, 6, 10, 12, 16, 23, 28, 29, 30,

33, 34, 35, 38, 39, 40, 41, 42, 43, 44, 45,47, 48, 49, 50, 51, 52, 53, 55, 56, 59, 60,62, 63, 64, 66, 68, 71, 74, 75, 77, 78, 79,109, 116, 124, 125, 126, 127, 136, 139,141, 142

nitrogen accretion 53nitrogen cycle 12, 23, 50, 56, 59, 62, 63,

71, 74nitrogen fixation 4, 16, 33, 39, 41, 43, 47,

48, 49, 50, 59, 127, 136nitrous oxide 28, 74, 134nutrient cycle 12, 34, 35, 37, 56, 57, 59,

64, 69, 70, 73, 74, 127oil palms 79, 80overgrazing 13, 16, 22, 26, 76, 80, 81,

106, 124, 135Oxisols 4, 10, 33, 49, 63Panicum 17, 23, 66, 71, 88, 95, 113Panicum maximum 17, 23, 66, 71, 88, 113Paraguay 97Paspalum 17, 21, 50, 65, 83, 84, 95, 106,

137Paspalum notatum 17, 21, 65, 83, 106,

137pastures 2, 4, 6, 7, 9, 10, 11, 12, 13, 17,

18, 19, 20, 21, 22, 23, 25, 26, 27, 28, 29,31, 34, 36, 37, 38, 42, 43, 45, 46, 47, 50,52, 53, 54, 55, 56, 59, 60, 61, 62, 63, 67,68, 69, 70, 71, 73, 74, 75, 77, 78, 79, 80,81, 82, 83, 85, 86, 87, 88, 92, 94, 95, 96,97, 99, 100, 105, 106, 107, 108, 109,110, 111, 112, 113, 114, 117, 123, 124,128, 129, 133, 134, 137, 141

Pennisetum clandestinum 93Pennisetum orientale 48Pennisetum polystachyum 48Peru 14, 36, 56, 75, 82, 92, 104pest control 33, 36, 69, 87, 88, 89, 90, 91,

96, 102pest development 98, 142


pest resistance 87, 88, 102pests 3, 17, 18, 19, 23, 32, 36, 53, 69, 87,

88, 91, 94, 95, 96, 97, 98, 99, 100, 101,130

Philippines 39, 40, 45phosphorus 6, 11, 33, 34, 40, 41, 47, 49,

52, 53, 56, 59, 67, 70, 72, 73, 75, 78, 79,106, 113, 114, 115, 124, 125

Piezodorus guildinii 18, 91plant competition 39, 55, 115, 128plant succession 81, 111, 128pollination 103, 116, 117pollution 59, 74, 106, 139, 141polyphenolics 8, 16, 44, 56production level 30, 62, 74, 139, 141Pueraria 14, 18, 41, 45, 47, 48, 49, 50, 65,

66, 84, 89, 96, 104, 113, 143Pueraria hirsuta 48Pueraria javanica 47, 143Pueraria phaseoloides 14, 18, 41, 45, 49,

65, 66, 84, 89, 96, 104, 113rangeland 15, 61, 65, 75, 80, 109, 111,

112, 113, 116, 118, 123, 129, 130reclamation 110, 114, 116reforestation 21, 80, 105, 106, 110, 111,

116, 134regeneration 2, 3, 4, 23, 24, 55, 75, 76, 92,

105, 109restoration 9, 29, 32, 41, 43, 110, 113, 115revegetation 23, 24, 29, 32, 105, 106, 109,

110, 111, 112, 113, 114, 115, 116rhizobia 5, 109, 110, 116rice 28, 36, 44, 45, 47, 67, 92, 93, 94, 140rodents 24, 98, 125rotational grazing 83, 96Rwanda 50, 57savanna 4, 35, 49, 52, 57, 59, 67, 72, 73,

84, 113, 120, 130, 133, 135, 141seed production 19, 55, 58, 96, 101, 124,

125seeds 16, 24, 26, 36, 37, 55, 58, 78, 94,

95, 98, 101, 102, 106, 113, 116, 126,127, 129, 142

semiarid zones 82, 117Sesbania sesban 39, 41

sheep 27, 40, 62, 67, 78, 82, 86, 112, 123,138

shifting cultivation 4, 13, 35, 36, 40, 41,55, 69, 70, 104, 131, 134

shrubs 13, 15, 17, 34, 37, 40, 75, 76, 79,80, 86, 92, 108, 109, 112, 113, 116, 130,142

silvopastoral systems 24, 70, 79, 86, 105,108, 121

soil acidity 7, 22, 33, 42, 46, 48, 52, 54,59, 60, 61, 62

soil biology 31, 61, 68, 73soil biomass 67, 71soil bulk density 8, 50, 66, 81soil chemical properties 33, 34, 35, 36, 38,

41, 42, 45, 48, 49, 54, 57, 59, 60, 61, 65,68, 70, 71, 75, 77, 106, 112, 137

soil compaction 8, 13, 40, 59, 81, 82soil erosion 8, 15, 22, 37, 38, 40, 49, 55,

58, 75, 76, 78, 79, 80, 84, 103, 104, 106,108, 112, 136, 142

soil fauna 9, 67, 73soil improvement 9, 32, 37, 41, 45, 77soil organic matter 4, 29, 36, 41, 42, 45,

46, 47, 48, 50, 56, 64, 71, 80, 137soil organisms 9, 49soil pH 6, 7, 34, 46, 48, 54, 60, 61, 62, 63,

114, 143soil physical properties 14, 36, 48, 49, 64,

65, 66, 68, 71, 77, 81, 82, 112soil properties 2, 3, 13, 36, 37, 38, 41, 47,

50, 53, 54, 63, 66, 71soil salinity 105, 107, 108, 112soil structure 8, 9, 14, 38, 47, 55, 64, 65Somalia 75sorghum 39, 57, 58, 77, 78, 89, 91Sorghum bicolor 57, 58, 78, 89South America 28, 33, 40, 52, 56, 70, 81,

82, 91, 96, 97, 99, 100, 103, 111, 129,134, 137, 141

South East Asia 40, 140soybeans 66, 91species diversity 25, 27, 31, 67, 68, 73, 87,

103, 111, 112, 118, 119, 120, 121, 122,124, 125, 126, 129, 130, 131


Spondias mombin 110Sri Lanka 49stocking rate 12, 20, 25, 26, 59, 62, 80, 81,

109, 124, 125, 136Stryphnodendron pulcherrimum 110Stylosanthes 15, 18, 41, 45, 46, 47, 49, 50,

51, 53, 55, 66, 77, 82, 88, 92, 96, 99,100, 102, 104, 114

Stylosanthes capitata 49, 100Stylosanthes hamata 55, 114Stylosanthes humilis 53, 77Stylosanthes macrocephala 49Stylosanthes scabra 92Stylosanthes viscosa 92succession 81, 111, 115, 116, 123, 124,

128sugarcane 123sustainability 10, 22, 27, 33, 34, 37, 40,

41, 42, 43, 45, 52, 54, 59, 60, 61, 64, 67,69, 70, 75, 79, 80, 86, 88, 108, 109, 110,113, 117, 118, 121, 123, 124, 128, 130,131, 141

Swietenia macrophylla 110, 111swine 37, 123, 141Tanzania 72, 120, 142Tephrosia candida 34, 35, 48Tephrosia vogelii 142Thailand 46tomatoes 89trees 4, 15, 17, 21, 32, 34, 35, 37, 40, 42,

49, 56, 57, 65, 69, 70, 77, 79, 80, 84, 86,87, 92, 106, 108, 110, 111, 112, 113,122, 123, 131, 135, 142, 143

Trifolium pratense 117tropical forest 4, 12, 25, 36, 40, 59, 69, 70,

71, 74, 75, 81, 82, 103, 104, 110, 111,

113, 119, 121, 122, 123, 131, 132, 133,134, 135, 137

tropical highlands 46, 50, 80, 93, 106, 142tropical savanna 35, 52, 72, 73, 113, 130,

135tropics 4, 13, 16, 23, 26, 32, 33, 36, 37,

40, 42, 61, 76, 77, 78, 83, 84, 86, 97,104, 107, 108, 109, 119, 124, 129, 130,132, 136, 137

Turkmenistan 86, 112Ultisols 4, 10, 33undersowing 39USA 36, 96, 99, 100, 103, 113, 120, 138VAM 6, 9, 13, 23, 114, 115vegetation change 129Venezuela 20, 67, 70Vigna trilobata 58, 77, 78water pollution 106water quality 20, 22, 31, 75, 106water salinity 105, 108watershed 14, 75, 104, 106weed control 33, 83, 93, 94, 142weeds 3, 14, 17, 18, 26, 33, 36, 37, 40, 41,

55, 72, 77, 92, 93, 94, 95, 128, 129, 142,143

West Africa 39, 45, 72, 76, 86wheat 18, 43, 44, 54, 88, 91, 109, 140wild birds 130windbreaks 14, 15, 17, 76, 85yield components 102yields 5, 13, 29, 33, 34, 35, 36, 37, 39, 40,

41, 43, 46, 48, 49, 50, 51, 53, 54, 55, 57,58, 59, 63, 66, 72, 74, 78, 79, 80, 85, 86,88, 90, 92, 93, 100, 101, 102, 105, 106,112, 113, 114, 123, 124, 138, 141, 142

Zornia glabra 49Zornia latifolia 99

ecological impact of tropical pastures and the potential...

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